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What causes people to believe in conspiracy theories?

7 Post author: Servant 07 May 2011 12:06AM

I'm sorry if this post doesn't seem that high quality, but I do feel this might be the best place to ask. The point of this post is to inspire discussion, hopefully discussion that might be useful for answering certain questions I had.

On another board, I gathered evidence of the existence of  "mainstream" conspiracy theories with the goal of figuring out why those conspiracy theories are, well, mainstream. Part of the problem is that, because they're mainstream, many people here may believe in them and may even contest the idea that they are even conspiracy theories. I don't really want to get into arguments over if a conspiracy theory is true or not, so just remember "Politics Is The Mindkiller".

1) JFK was assassinated in a conspiracy. (75% of Americans believe this according to a 2003 Gallup poll.)

2) Martin Luther King, Jr. was assassinated in a conspiracy. (58% of Americans believe this according to a 2008 CNN/Essence poll.)

3) Bush lied about WMDs. (43% of Americans according to a 2005 Pew Survey, only 41% disagreed with this statement, according to a 2005 Pew Survey.)

4) No international consensus on who did 9/11, with 49% of Mexicans, 66% of Egyptians, 40% of Turks, 52% of Jordanians and 55% of Palestinians naming a suspect other than al-Qaeda. This is from a 2008 World Public Opinion poll (graph below).

It's clear that at least some conspiracy theories are treated as mainstream in at least some polities, but other conspiracy theories, like "Americans hoaxed the moon landing" are fringe (only 6% of Americans believe this, according to a 2001 Gallup poll [link here]). In fact, many bloggers, including the economist Robin Hanson, labor under the idea that all conspiracy theories are fringe and wonder why are these individuals so different from the "mainstream". So here's two questions that I would like answered, because these results had been bugging me:

1) There is some sort of method by which an individual can 'filter' out the false and "fringe" conspiracy theory while then selecting a 'true' and "mainstream" conspiracy theory to be accepted. What factors play into an individual's decision-making process to determine what conspiracy theories to accept and what to reject?

2) Is the process of believing in conspiracy theories impacted by some form of rationality? Does Bayesian logic plays a role here as well...do individuals unconsciously rate the likelihood of a conspiracy theory and accept conspiracy theories with a high probability of it occurring (while rejecting conspiracy theories with a low probability of it occurring)?

Addendum: (I tried to select examples that could generally be agreed to be "conspiracy theories" to avoid arguments over definitions that I'd lose, but I may have failed in this sort of thing. To reveal bias, I believe that a conspiracy theory is a hypothesis about a covert plot by more than one individual.)

Comments (45)

Comment author: Jayson_Virissimo 07 May 2011 01:00:57AM *  15 points [-]

When people use the term conspiracy theory, they usually mean false conspiracy theory. This is confusing terminology because in the archetypical examples, the "official story" actually involves a conspiracy.

Comment author: candid_theist 07 May 2011 05:32:04PM 4 points [-]

Right. I for one happen to believe the theory that al Qaeda conspired to execute deadly attacks on Sept. 11, 2001. That is literally a conspiracy theory. Is the process by which I came to believe that relevant to the discussion here? (If yes, I'd be happy to give more information.)

But the phrase "conspiracy theory" commonly implies (like the faked moon landing) that relatively few people believe it, generally because the evidence against the theory is fairly convincing. (Conspiracists may answer that additional evidence is not available or widely known to the public.)

Comment author: gjm 07 May 2011 08:35:16PM 5 points [-]

What's distinctive about "conspiracy theories" is generally not so much the alleged conspiracy to do whatever-it-is but the conspiracy to hide their having done it. And, usually, the fact that it would have to be an exceptionally effective conspiracy, because keeping such things secret is often difficult.

Comment author: TheOtherDave 07 May 2011 09:20:30PM 2 points [-]

And, related to this, the epistemic pattern whereby anyone who ought to know the facts of the situation and claims my theory is false must therefore be part of the conspiracy.

Comment author: Vladimir_M 07 May 2011 06:20:22PM *  10 points [-]

I can think of two common and closely related patterns of delusional conspiracy theories that are nevertheless plausible to great numbers of people. (These are not the only ones, of course.)

The first pattern occurs when large groups of people express beliefs and perform acts that are systematically biased in a certain direction and effectively further some clearly recognizable interests and goals, and yet there is no consciously organized coordination among them. Such situations often occur because humans are instinctively attracted towards opinions and acts that signal high status and affiliation with prestigious groups. Yet for many people it's hard to believe that such spontaneous decentralized coordination is possible, so they seek explanation in conspiracy theories.

So, for example, the mainstream media often exhibit strong and practically uniform bias in their coverage of politicians, events, and issues. Thus, for many people it's tempting to assume that they are indeed under some centralized editorial command. Depending on their ideological inclinations, they may imagine these commands coming from boardrooms of nefarious media tycoons, or perhaps (for even loonier types) from scheming cabals of Jews. Yet in reality, even the strongest and most uniform biases simply reflect those beliefs that are considered high-status among the sort of people that tend to work in the media -- and the prevalence of this sort of people is itself not a matter of any conspiracy or centralized control, but a spontaneously originating and self-perpetuating artifact of normal human social behavior.

The second, closely related pattern occurs when people detect correctly that they are getting cheated, lied to, or screwed over by the elites in charge, but are unable to analyze accurately what's going on. (These actions may actually be conspiratorial to some degree, but more often it's a matter of spontaneous coordination as in the above example.) In many instances, an accurate analysis of the situation would be too complicated for the average person, while intellectuals risk their own status if they realize the truth and speak it openly (attacking the elite opinion is by definition a status-lowering move). Thus, people end up creating conspiracy theories that have some vague kernel of truth in them, but are a gross and simplistic caricature of what's really going on. In turn, intellectuals are happy to use these laughable caricatures as convenient strawmen for attacking their more sophisticated critics.

For example, the conspiracy theories that flourished in the Second Red Scare (a.k.a. "McCarthyist") period in the U.S. were a consequence of a very real record of misdeeds, blunders, covert dealings, ideological delusions, and sometimes even real espionage and treason among the American political and intellectual elites. Yet the popular awareness of these problems found its expression in naive and grotesque grand conspiracy theories à la General Ripper, which were a ridiculous caricature of the complicated and bizarre reality -- in which actual conspiracies were far from absent, but a relatively minor factor in the big picture, which was as usual determined by the regular human patterns of social behavior and status-seeking, and the systematic biases and spontaneously coordinated actions following from them.

Comment author: JoshuaZ 07 May 2011 03:29:31AM 6 points [-]

A lot of good comments have already been made, but I'd like to mention another issue (that is by the way quite an old point and not original to me. I think Martin Gardner made the point many years ago, and Michael Shermer is often fond of it.) People are overactive pattern seekers. We seek to see large patterns where they don't necessarily exist. Moreover, this gives people comfort because people don't like a complicated, difficult to understand universe with lots of random events. Take that with a healthy dose of confirmation bias and you get the end result.

Comment author: timtyler 07 May 2011 08:50:05AM 2 points [-]
Comment author: Eugine_Nier 07 May 2011 02:59:59AM 6 points [-]

One factor to consider is that in non-open societies, people are used to being fed lies, frequently blatant lies, by official sources. Thus we should expect people in those societies to be more skeptical of "official sources" and "official stories" more generally. Furthermore, if said source isn't their own government, they may feel more free to openly express this skepticism.

Comment author: scientism 07 May 2011 03:21:14PM 5 points [-]

I think conspiracy theories are comforting. Most conspiracies involve the government. In the modern world, our government leadership doesn't stand for anything or serve any higher purpose, at best they stand stand for non-things (i.e., freedom and democracy, which are essentially constraints imposed on government). For many people it's more comforting to think that their government is malevolent than to face the reality that it's a powerless, directionless bureaucracy.

Comment author: nazgulnarsil 07 May 2011 12:48:39AM 4 points [-]

People treat "conspiracy theories" as a reference class and then when one turns out to be true or partially true they raise their estimation of others being true.

Comment author: Caerbannog 07 May 2011 03:15:08AM 3 points [-]

It seems that people are more likely to believe conspiracy theories that already are in line with their worldview. This would be an example of confirmation bias, to an extent.

People are also more likely to believe a particular conspiracy theory if they hear it from someone whose opinion they already respect, or if many others in their social group believe such a theory.

I don't believe rational decision-making plays much part in the acceptance of conspiracy theories. You note that only 6% of Americans believe that the moon landing was hoaxed, and consider that an example of a fringe theory. Note, however, that about a quarter of Russians and English people think the moon landing was hoaxed.

It seems that what's considered fringe varies by population, and not necessarily by rationality or evidence. It makes me wonder if there are any theories believed by most Americans that are considered ridiculous elsewhere.

Comment author: DanielLC 08 May 2011 04:08:18AM 2 points [-]

Something more in line with your worldview is more likely. This is the point of a worldview.

Someone whose opinion you respect is more likely to be right. This is the point of respecting people's opinions.

What's the irrational decision-making you're alluding to?

Comment author: Caerbannog 09 May 2011 04:06:52PM 0 points [-]

Your worldview and your choice of people whose opinion to respect don't have to be selected rationally. I would argue, in fact, that a large proportion of people don't choose these rationally.

An alarmingly large fraction of Americans believe that the earth was created 6000 years ago, a position that most people here would find irrational. This is a worldview that is most often acquired from one's parents or from respected religious figures. Would such a worldview be considered to be rationally selected?

Other people hold the position that humans evolved from earlier primates over millions of years through evolution by natural selection. Many of these people don't understand evolution well enough to hold it as a rational belief, and they may also have acquired this belief through their parents or other respected figures rather than by a reasoned analysis. I've been asked by someone who accepts evolution: "Wouldn't it be great if humans would evolve wings! That would increase fitness, why doesn't that happen?" [paraphrased]

I think it's not controversial to say that peoples' worldviews and authority figures are not selected rationally.

Comment author: DanielLC 09 May 2011 07:00:42PM 0 points [-]

True, but the way they irrationally found those is what's in error, not using them. This is sort of like having a bad prior and blaming Bayes' Theorem.

Comment author: ciphergoth 07 May 2011 01:13:12PM 2 points [-]

It would have been good to include a few entries here along the lines of "President Nixon tried to cover up the role of his re-election campaign in the Watergate break-in".

Comment author: Vladimir_M 07 May 2011 09:38:02PM *  12 points [-]

Or, for example, the theory that a head of state could have illegally circumvented U.S. law by falsely claiming to be a natural-born citizen based on a fake Hawaiian birth certificate.

Haha, sorry couldn't resist. Just in case, I beg everyone to click on the links before downvoting...

Comment author: CarlShulman 07 May 2011 10:38:42PM 2 points [-]

That's hilarious.

Comment author: JoshuaZ 07 May 2011 03:06:31PM 2 points [-]

It would have been good to include a few entries here along the lines of "President Nixon tried to cover up the role of his re-election campaign in the Watergate break-in".

Hmm, this leads to an idea that maybe should go over in the experiment thread- see how good the general population is in saying they believe in actual conspiracies.

This does lead to a serious issue though, how do we distinguish the actual conspiracies from the non-conspiracies? See for example Cracked's Seven Insane Conspiracies That Actually Happened.

It seems that the set of actual conspiracies is much smaller than the set of claimed conspiracies so the prior is in general low. Also, most actual conspiracies are comparatively small scale and involve short-term interests compared to the general pool of conspiracies. However, there are some conspiracy theories that fall into this pattern that are generally considered to be in the crazy category- the most obvious two would be 9/11 conspiracy theories and JFK assassination theories. Thus, without actually looking at the evidence and motivation, it may be genuinely difficult to distinguish between the real and imagined conspiracies.

Comment author: CronoDAS 08 May 2011 05:36:00AM 4 points [-]

According to what I read on Wikipedia, it's not clear whether the "Business Plot" actually existed in any real sense... apparently, there's no evidence of it other than Smedley Butler's testimony.

Comment author: benelliott 07 May 2011 03:14:58PM 3 points [-]

Thus, without actually looking at the evidence, it may be genuinely difficult to distinguish between the real and imagined conspiracies.

This is certainly true of any other kind of theory, why should it be different for conspiracies?

Comment author: JoshuaZ 07 May 2011 03:19:45PM 1 point [-]

This is certainly true of any other kind of theory, why should it be different for conspiracies?

Well, there are large classes of theories where almost all of them are just wrong to the point where we don't need to bother investigating more of them at all. Thus for example, there are a lot of ideas about sympathetic magic where the priors are so low that we don't need to check the claims. Similar remarks apply to ideas that require minds to be irreducible ontological entities.

Comment author: benelliott 07 May 2011 03:37:55PM 3 points [-]

Fair point. However, most conspiracies, while implausible and tied down with many burdensome details, do not actually violate physics as we know it.

Comment author: saturn 07 May 2011 09:06:50AM 2 points [-]

Your questions seem ambiguous. Do you want advice about how to evaluate conspiracy theories, or do you want to know how conspiracy theories come to be popularly accepted or rejected?

Comment author: Servant 08 May 2011 02:48:04AM 1 point [-]

While I am more interested in the latter, the former is likely the one more suited for the main goal of this "community blog".

Comment author: fubarobfusco 07 May 2011 02:43:15AM 2 points [-]

"Conspiracy theory" doesn't really seem to me to be a topic of belief, but rather a way of responding to events. It seems to involve looking at a negative outcome and thinking of whom to blame for it, and how to make that blame stick, rather than trying to actually come up with truth-tracking explanations.

Comment author: Eugine_Nier 07 May 2011 02:56:22AM 6 points [-]

Interestingly two of Servant's examples aren't so much about finding an out-group to blame as deflecting blame from an in-group.

After his death, JFK became a martyr for a lot of people on the anti-war left. As such his having been assassinated by a communist sympathizer and former defector to the USSR was rather inconvenient.

In the case of 9/11 especially in a number of the countries mentioned, the need to deflect blame is even more obvious.

Comment author: jhuffman 07 May 2011 12:36:16PM *  1 point [-]

Why do you think so many Germans (25%!) think the US Government is responsible for the 9/11 attacks?

Comment author: Vladimir_M 07 May 2011 09:48:47PM 4 points [-]

Outside the U.S., and even in some circles inside the U.S., anti-Americanism is a popular and cheap status-signaling attitude. (Moldbug wrote a good analysis of the phenomenon a while ago.) Clearly, in more sophisticated circles it usually has subtler forms, but among the common folk it often has rather crude expressions such as this one.

Comment author: FAWS 07 May 2011 11:34:16PM *  1 point [-]

Similarity to the Reichstag Fire and the subsequent Enabling Act perhaps? The Reichstag fire probably wasn't laid by the Nazis themselves either, but since they enormously profited from it politically many people believed (and I guess still believe) that they did it.

Comment author: mutterc 07 May 2011 11:41:28AM 2 points [-]

Spot-on with the conspiracy theorists I deal with most in real life, as parent of an autistic: anti-vaccination-ers.

Raising children does funny things to human cognition (for good evolutionary reasons). Raising a disabled child is even tougher psychologically, and finding someone to blame (in their case, amoral-profit-seeking Big Pharma and regulatory capture) provides psychological comfort.

Comment author: jhuffman 07 May 2011 12:38:27PM 1 point [-]

I see this less as blame deflection (since there is no official narrative to refute) and more of a frustrated pattern matching mechanism. The rise in autism rates is baffling and demands an explanation, and people who are close to the issue are going to seize on one just to protect their own psyche from relentless and fruitless questioning.

Comment author: benelliott 07 May 2011 11:47:31AM 1 point [-]

How does this account for Moon Landing conspiracy theories?

Comment author: fubarobfusco 07 May 2011 06:20:57PM 2 points [-]

Good point: the class of "X didn't really happen" conspiracy theories doesn't seem to fit the above pattern "Find someone to blame for negative outcome Y".

Well ... maybe it does. I'm not sure if I'm not just playing with definitions here to defend my previous claim, but I'll run with it ...

The conspiracy theories that assert that "X didn't really happen" are of the form Y = "The mainstream has been convinced of false claim X". In other words, the conspiracy theory attempts to explain not merely why X is false, but why the mainstream believes X is true ... and to attribute blame for this presumably negative state of affairs.

Moon-landing deniers don't merely assert that "the moon landing didn't happen", but rather "the government, Hollywood, etc. conspired to convince the public of the false claim that the moon landing did happen".

Similarly, conspiracy-minded creationists do not merely assert "evolution is false", but rather "the Darwinist atheist science teachers tricked people into thinking that evolution is true." Holocaust deniers do not merely assert "the Holocaust didn't happen", but "the Jews tricked the world into believing the Holocaust happened."

Notably, these conspiracy theories do not merely claim that X is false, but that X is an intentional hoax by some party, who is to be blamed.

Anyway, I may just be inventing terms to justify my previous overbroad claim. But here's a test: if we look at other "X didn't really happen" conspiracy theories, the above leads us to expect to find them blaming some particular party for convincing the public of X, in order to accomplish some conspiratorial goal.

Comment author: benelliott 07 May 2011 06:44:21PM *  1 point [-]

if we look at other "X didn't really happen" conspiracy theories, the above leads us to expect to find them blaming some particular party for convincing the public of X, in order to accomplish some conspiratorial goal.

Some sort of intentional deception is pretty much the only way you can explain the existence of lots of strong evidence that X happened if you wish to argue that it didn't, so I think the blame angle on those may just be out of necessity to make the whole theory hang together.

It also doesn't really fit the 'see a negative outcome, find someone to blame' because they didn't see a negative outcome, they invented one.

I'm not criticising your hypothesis, I think it works quite well to explain a lot of cases, but I think there must be something else that you're missing.

Comment author: candid_theist 07 May 2011 06:54:27PM 0 points [-]

This can just as well be "X did happen, but the mainstream has been convinced it did not." The theory that an extraterrestrial spacecraft crashed near Roswell, New Mexico comes to mind.

Or creationism can be seen as a combination: "Genesis 1-2 (X1) literally happened, but the atheist scientists invented evolution (X2) and tricked people into believing it."

Comment author: roland 01 November 2011 10:34:13AM *  1 point [-]

To reveal bias, I believe that a conspiracy theory is a hypothesis about a covert plot by more than one individual.)

What always bugs me: attibuting 9/11 to Bin Laden/Al Qaeda is as much a conspiracy theory as it is attributing it to the government. Yet generally only the latter is classified as a "conspiracy theory".

Comment author: JoshuaZ 01 November 2011 12:50:05PM 1 point [-]

No they aren't. When most people use the term "conspiracy theory" they generally mean larger scale, not obvious individuals, and with motivations that are more obscure. There's some level of denotation v. connotation here.

Comment author: TheOtherDave 01 November 2011 04:45:10PM 1 point [-]

I agree with you about connotations being relevant, but my sense is that the most important connotation here is "low status."

At least in the U.S., attributing 9/11 to Bin Laden/Al Qaeda is a relatively mainstream belief, as for a time was attributing it to Hussein/Iraq (although the two theories were not considered mutually exclusive among communities that embraced the latter); consequently we don't describe either as a "conspiracy theory" Attributing it to, say, Basque terrorists -- or even to the specific leader of an ETA cell, or whatever -- would be labelled a "conspiracy theory" if an otherwise unremarkable person did it, but not if the President did... or, more precisely, anyone who labelled it a "conspiracy theory" when the President did it would be attempting to lower the President's credibility/status by so doing.

Comment author: Desrtopa 07 May 2011 02:57:30AM 1 point [-]

3) Bush lied about WMDs. (43% of Americans according to a 2005 Pew Survey, only 41% disagreed with this statement, according to a 2005 Pew Survey.)

Well, the Downing Street Memo does seem to imply that he had already written the bottom line before the investigation into whether Iraq possessed WMDs had made much headway. He may well have believed that that Iraq possessed WMDs, but it seems that he had committed to the conclusion the public was going to be presented with regardless of the state of the evidence.

Comment author: JoshuaZ 07 May 2011 03:26:09AM 3 points [-]

Having the bottom line written already is not the same thing as lying. Neither is a good thing where rational dialogue is concerned, but the claim "Bush lied" has in most common moral frameworks a very different meaning than "By a host of systemic effects and severe cognitive biases, the Bush administration gave a deeply inaccurate summary of the situation." In order to be better rationalists we need to try to be aware of how frequently apparent lies are likely just severe biases.

Comment author: Desrtopa 07 May 2011 03:38:06AM 2 points [-]

But deliberately misrepresenting the data in order to support a particular conclusion, that which the memo alleges, is lying about the state of the evidence, whether he and other members of the administration believed the conclusion or not.

Comment author: JoshuaZ 07 May 2011 03:57:20AM *  1 point [-]

But deliberately misrepresenting the data in order to support a particular conclusion, that which the memo alleges, is lying about the state of the evidence, whether he and other members of the administration believed the conclusion or not.

This is interesting, in that having reread the memo, I still don't see it as saying that the data was deliberately misrepresented, and having just reread the Wikipedia page, I still don't get that attitude. I don't think this is due to bias on my part, since if I have any biases in this regard it would be biases that would make me want to think that Bush lied.

The memo says things like:

Bush wanted to remove Saddam, through military action, justified by the conjunction of terrorism and WMD. But the intelligence and facts were being fixed around the policy.

That doesn't sound like deliberate lying to me. The administration had massive systemic problems. This isn't the only example of this problem. A substantial fraction of the administration seemed to think that their personal wishes effectively determined what reality would do. (See for example Rove's comment about the "reality-based community").

It is difficult to underestimate human capacity for mendacity but it is equally hard to underestimate human capacity for self-deception.

Comment author: timtyler 07 May 2011 09:45:16AM 1 point [-]

Marshall Brain once wrote a nice conspiracy-theory article.

Comment author: Hyena 07 May 2011 05:31:01AM *  1 point [-]

I think conspiracy theories aren't born from a single process. Some, I think, have a clear positional motive. Others defend a worldview, e.g. many Truthers may be defending an "invincible America" mythos. These would be "motivated" conspiracies: they are bound uo with affect and sentiment.

But a lot of theories are probably poor reasoning: spurious patterns, attribution error, false perceptions. I think the JFK and MLK theories are false perceptions for most people who didn't live through them, believers fail to understand just how easy it was for one man to carry it out. When you understand that, Hollywood looks absurd and the Secret Service a good order of magnitude less paranoid.

I think that UFO conspiracies are false perceptions, namely, of how culture and media can work together to create a phenomenon out of thin air and make it seem incredibly common. People don't or didn't estimate this well.

Comment author: JeffFisher 19 May 2014 12:38:24AM 1 point [-]

I fell into conspiratorial thinking when I was less experienced in the ways of the world. Noticing that a dark OD green helicopter with subdued markings could easily be mistaken for an unmarked black helicopter when viewed against a bright sky by an untrained observer was the start of finding my way out of that one. I remember that some things that were claimed I recognized immediately (everyone has seen black SWAT uniforms, for example) and this created a sense of credibility, while others I suspected (I was anti-internationalist back then), and I didn’t have direct knowledge of others so I didn’t try to evaluate those things but instead gave the theory a pass when it came to those. It didn’t seem like an aberration at the time, but I didn’t know about the conjunction fallacy back then. The theory certainly reinforced the beliefs I held back then, and it also gave me a feeling of superiority because I knew a secret. Yup, I was a sucker.

I've come to notice that conspiracy theories tend to be based on two or more things that are known or believed to be true, but that are not normally expected to be linked. These are then joined by a pretext for linking them in a way that would be considered outrageous to anyone that doesn’t hold the theory—some of these details are often completely inconsequential of themselves and do not necessarily add anything of substance to the theory, but adding a few high-probability elements skews the conjunction fallacy in the theory’s favor. It is worth noting that sometimes major parts of a theory are not known, but classic propaganda techniques like the “big lie” are used to cause us to evaluate their probability more highly than we should. The latter is not strictly necessary though due to the power of the conjunction fallacy. Today I take it as a red flag when I see a linkage being formed between one thing that is obvious and another that is obvious, but where the linkage is tenuous. If you have to ask “where are you going with this” the answer probably isn’t good.

This linkage is then applied to combine the theory with multiple things that are not known but are either suspected by the individual or group, or are inspired by the theory, and that can be linked by conjecture to the concept of the conspiracy. Once the basic linkage is accepted the conjunction fallacy keeps rolling and that high probability that is erroneously given to the initial theory then gets associated with all of the other craziness.

A fake conspiracy theory can demonstrate how the conjunction fallacy plays into this. "We know that we orbit the sun, and we know the sun causes skin cancer, but did you know that the earth, sun, and human race were created by ancient aliens as part of a skin cancer experiment?" Our intuition evaluates that by giving 100% to the first two things, and since we can't know the third we mentally skip it which would be like giving it 0% probability, but that's okay because 100% + 100% + 0% = 200% probability so we are believers now. Once we are believers, we give the entire idea 100% likelihood, so we know that all of the components have to be true so they all have 100% likelihood in our mind and now we know that we are alien skin cancer test subjects. But if that is true then sunscreen was probably invented by the aliens as part of their testing protocol because otherwise, why would they let us use something that would reduce our chance of getting skin cancer? So now we know that sun screen is a perverse part of the alien plot and we refuse to buy it and try to convince our friends that it is evil.

Obviously, we should instead be multiplying probabilities, where 100% * 100% * 0% = 0%. But that isn't the way most people tend to think. Instead most people rely on whether or not one of the foundational contexts of the theory contradicts or supports their biases, so most people who don’t follow conspiracy theories are probably not doing so because they made the correct calculation of probability but because they “know” one of these things can’t be true. For example, a geocentrist would reject the theory since they “know” that the earth doesn’t orbit the sun, while a creationist would reject it outright because they know God created the earth not aliens. However, the geocentrist might start their own branch of the theory though, like the many branches of the JFK assassination theory. For example, I suspect that one reason the Moon landing conspiracy has so few adherents is that there are so many ideological positions that it violates, even ones that tend to be mutually exclusive demographically. For example, the American right are likely to reject it because it is anti-American, while the American left are likely to reject it because it is anti-science. If everything about the moon landing were identical but the Soviets had got there first, I suspect that the American right would embrace it at rates similar to young-earth creationism.