Of course there are less people who were killed for their faith than people who were not killed, I wasn't contesting this.
You should be. Let's review. Your first comment was http://lesswrong.com/r/discussion/lw/m0l/is_belief_in_belief_a_useful_concept/c89r , in which you quoted the claim
a person does not notice much harm from believing the Messiah is coming
and objected, 'martyrs!':
Say that to the countless martyrs, especially in Roman times, who could have evaded torture and death just by publicly saying "I no longer believe" (even if they continued to believe in secret).
Now. How do martyrs show that believing in the Messiah is harmful? If something is harmful, then it should make one more likely to die compared to someone who doesn't believe in the Messiah, such as an atheist; however, it's a well-known epidemiological result that the relative risks of believers and non-believers tends to go the other way ie. religious believers (such as Christians and other groups who believe in the Messiah coming) live longer. This is true on a population level, so however many martyrs there are these days, however many morons go to North Korea with delusions of conversion, they do not move the needle; to the extent we want to make any inference about the effects of believing in a Messiah, we would say that believing in a Messiah is healthy, and if something is healthy, one indeed will not 'notice much harm'. One could ask, if martyrs are dying for their beliefs and this is inherent to believing in a Messiah on its own, why are all the other believers (who also believe in the Messiah) not dying for their beliefs?
OK, maybe current figures are unrepresentative and in other periods believing in a Messiah would have had noticeable decreases in correlated life expectancy. While the records of Christian persecution are light on details and headcounts (unsurprising for a brief and half-hearted persecution, of minimal interest to outsiders and poorly documented due to its unimportance, which has been hyped a great deal by certain parties whose interest is understandable), my understanding is that the most realistic estimates of the 'countless' martyrs, based on Eusebius's count, extrapolate to figures in the thousands, not millions. In an empire with a population of 58 million+, this is not noticeable, and given the described mechanics of the persecution in which 'victims' could usually trivially escape punishment, it would be astounding if it were noticeable. (How many victims would Stalin/Mao's gulags and secret police and famines have claimed if one could escape any punishment by simply saying "why yes, I am a communist!" ) Expecting it to matter would be as ridiculous as pointing to the martyrologies (if I may borrow the term) of Travyon Martin et al and saying police killings are a major reason for why black males have shorter life expectancies in the USA (which of course they don't, as that's affected much more by issues like increased heart disease rates).
Since all that shows belief qua belief is harmless or outright healthy, that resolves your objection as simply wrong. The rest is tangents.
But that does still leave an issue as to why a handful of weirdos chose suicide-by-praetor as exemplified in my anecdote, and for that I suggest a toxic mix of status-seeking, mental illness, dangerous auxiliary beliefs ("I believe in the Messiah and that by dying I ... [hasten his coming / spread the Gospel / whatever]"); none of these may strike you as particularly plausible or likely, and none of these explanations explain all of the martyrs simultaneously, but that's fine, since for extremely rare outliers (as martyrs are), there will not usually be any universal explanation and the true explanations will nevertheless be extremely unlikely a priori. (Since my airplane example apparently didn't convey my point, consider a lottery; the chance of a particular number winning is extremely unlikely and no number wins many times, yet someone will win with some number.)
Do you think that all (or most) missionaries who go to a dangerous area, do it with the explicit purpose of getting killed, and do not believe in their cause?
I think for many of them there is a definite death-seeking component to the psychology which made them seek out that dangerous area when there's an entire world to choose from, and that martyrdom and talk of sacrifice attracts those people in particular. This is visible right down to the rhetoric.
About your North Korean example, it's not the example I asked for, as they didn't just go directly to an officer or a border guard to announce their faith, I have an educated guess that they would continue their work and take at least some steps for not being found out. But let's suppose I was wrong. Even if we assumed that the missionaries going to north Korea don't believe in their cause and are doing it just because they want to commit suicide and are just lazy or afraid to hang themselves,
The record of missionaries to NK is not good. They are routinely captured and executed. Clearly, whatever precautions they are taking do not work very well. So why do they do it? Are they just too stupid to realize the danger and that their precautions are insufficient? Well, the exact reason will differ from outlier to outlier...
what do you think about people who are not actively seeking danger, and are killed by death squads because of their beliefs?
Confounded by the many reasons for killing people: cultural, economic, ethnic, governmental. Because religion lines up with so many other divisions (religion is not about belief...), I am doubtful there are many clean cases of religion-only genocide. There are few instances where persecution stops immediately upon recanting - to give some examples, simply converting to Catholicism was not enough to save Jews in Nazi Germany, simply declaring oneself an atheist did not exempt Jews from persecution in the USSR, etc.
By your logic, there are much fewer mountain climbers than people who don't climb mountains, and mountain climbers are much more likely to die a violent death than the average people. Nevertheless, there are fewer mountain climbers who died during their expedition than those who didn't. Does this mean that the mountain climbers climb mountains because they seek death as their primary reason, and those who died, died because of this? Or that they accept falling from a cliff as a risk, and are climbing the mountain because they love it, not because they want to die?
I'm glad you chose that example, since that is one of the better ones for illustrating my point. Imagine a group of mountain enthusiasts, some of which climbed them and some of which expressed their interests in other ways. The handful of climbers frequently die gruesome deaths ("5,656 times with 223 deaths"), and when one looks at life expectancy, the climbing group does indeed live shorter lives, leading to descriptions of key holy sites for these enthusiasts as a "high-altitude lunatic asylum"; one psychology book notes, after discussing various studies correlating mental illness & suicide attempts with risk-taking behavior, that "The person who plays Russian roulette has a one in six chance of dying; the person who climbs Mount Everest has a one in ten chance of dying. Is it suicidal to attempt that climb?" (leading into, amusingly, a mention of early Christian martyrs and the Malay running-amok syndrome). If we looked at the climbers faction of the mountain enthusiast group and asked whether they were 100% psychologically normal, if there was no way we could distinguish them, if they appreciated and liked mountains in the same way as everyone else, we would likely have to answer... no. They are different. What is different probably differs from person to person (to give a LW-relevant example, the CEO of the Intrade prediction market died climbing Mount Everest - the same day his wife was giving birth, IIRC - and his death seems to have led to the exposure of substantial embezzlement or other fraud on his part and the shutdown of Intrade; one has to wonder if there was any connection between his hobbies and professional activities), but it would be bizarre to claim that simply liking mountains is harmful when it's clearly more specific than that; I like mountains, but I don't expect to ever die on one.
I am not sure that it is productive to tell certain people that they do not really believe what they claim to believe, and that they only believe they believe it. I have an alternative suggestion that could possibly be more useful.
Binary Beliefs
It seems that human beings have two kinds of beliefs: binary beliefs and quasi-Bayesian beliefs. The binary beliefs are what we usually think of as beliefs, simple statements which are true or false like "Two and two make four," "The sun will rise tomorrow," "The Messiah is coming," and so on.
Binary beliefs are basically voluntary. We can choose such beliefs much as we can choose to lift our arms and legs. If I say "the sun will rise tomorrow," I am choosing to say this, just as I can choose to lift my arm. I can even choose the internal factor. I can choose to say to myself, "the sun will rise tomorrow." And I can also choose to say that the sun will NOT rise. I can choose to say this to others, and I can even choose to say it to myself, within my own head.
Of course, it would be reasonable to respond to this by saying that this does not mean that someone can choose to believe that the sun will not rise. Even if he says this to himself, he still does not act as though the sun is not going to rise. He won't start making preparations for a freezing world, for example. The answer to this is that choosing to believe something is more than choosing to say it to oneself and to others. Rather, it is choosing to conform the whole of one's life to the idea that this is true. And someone could indeed choose to believe that the sun will not rise in this sense, if he thought he had a reason to do so. If he did so choose, he would indeed begin to make preparations for a dark world, because he would be choosing to conform his actions to that opinion. And he would do this voluntarily, just as someone can voluntarily lift his arm.
Quasi-Bayesian Beliefs
At the same time, human beings have quasi-Bayesian beliefs. These are true degrees of belief like probabilities, never really becoming absolutely certain of the truth or falsity of anything, but sometimes coming very close. These are internal estimates of the mind, and are basically non-voluntary. Instead of depending on choice, they actually depend on evidence, although they are influenced by other factors as well. A person cannot choose to increase or decrease this estimate, although he can go and look for evidence. On account of the flawed nature of the mind, if someone only looks for confirming evidence and ignores disconfirming evidence, this estimate in principle can go very high even when the objective state of the evidence does not justify this.
Belief in Belief
It seems to me that what we usually call belief in belief basically means that someone holds a binary belief together with a quasi-Bayesian belief which conflicts with it. So he says "The Messiah is coming," saying it to himself and others, and in every way acting as though this is true, even though his internal Bayesian estimate is that after all these thousands of years, the evidence is strongly against this. So he has a positive binary belief while having a very low estimate of the probability of this belief.
The reason why this often happens with religion in particular is that religious beliefs very often do not have huge negative consequences if they are mistaken. In principle, someone can choose to believe that if he jumps from the window of the tenth story of a building, he will be ok. In practice, no one will choose this on account of his non-voluntary Bayesian estimate that he is very likely to be hurt if does so. But a person does not notice much harm from believing the Messiah is coming, and so he can choose to believe it even if his internal estimate says that it is likely to be false.
A cautionary note: one might be tempted to think that religious people in general have belief in belief in this sense, that they all really know that their religions are unlikely to be true. This is not the case. There are plenty of ways to distort the internal estimate, even though one cannot directly choose this estimate. I know many very religious people who clearly have an extremely high internal estimate of the truth of their religion. They REALLY BELIEVE it is true, in the fullest possible sense. But on the other hand I also know others, also extremely devout, who clearly have an internal estimate which is extremely low: they are virtually certain that their religion is false, and yet in every way, externally and internally, they act and think as though it were true.