My intuition says presenting bad facts or pieces of reasoning is wrong, but withholding good facts or pieces of reasoning is less wrong. I assume most of you agree.
This is a puzzle, because on the face of it, the effect is the same.
Suppose the Walrus and the Carpenter are talking of whether pigs have wings.
Scenario 1: The Carpenter is 80% sure that pigs have wings, but the Walrus wants him to believe that they don't. So the Walrus claims that it's a deep principle of evolution theory that no animal can have wings, and the Carpenter updates to 60%.
Scenario 2: The Carpenter is 60% sure that pigs have wings, and the Walrus wants him to believe that they don't. So the Walrus neglects to mention that he once saw a picture of a winged pig in a book. Learning this would cause the Carpenter to update to 80%, but he doesn't learn this, so he stays at 60%.
In both scenarios, the Walrus chose for the Carpenter's probability to be 60% when he could have chosen for it to be 80%. So what's the difference?
If there isn't any, then we're forced to claim bias (maybe omission bias), which we can then try to overcome.
But in this post I want to try rationalizing the asymmetry. I don't feel that my thinking here is clear, so this is very tentative.
If a man is starving, not giving him a loaf of bread is as deadly as giving him cyanide. But if there are a lot of random objects lying around in the neighborhood, the former deed is less deadly: it's far more likely that one of the random objects is a loaf of bread than that it is an antidote to cyanide.
I believe that, likewise, it is more probable that you'll randomly find a good argument duplicated (conditioning on it makes some future evidence redundant), than that you'll randomly find a bad argument debunked (conditioning on it makes some future counter-evidence relevant). In other words, whether you're uninformed or misinformed, you're equally mistaken; but in an environment where evidence is not independent, it's normally easier to recover from being uninformed than from being misinformed.
The case becomes stronger when you think of it in terms of boundedly rational agents fishing from a common meme pool. If agents can remember or hold in mind fewer pieces of information than they are likely to encounter, pieces of disinformation floating in the pool not only do damage by themselves, but do further damage by displacing pieces of good information.
These are not the only asymmetries. A banal one is that misinforming takes effort and not informing saves effort. And if you're caught misinforming, that makes you look far worse than if you're caught not informing. (But the question is why this should be so. Part of it is that, usually, there are plausible explanations other than bad faith for why one might not inform -- if not, it's called "lying by omission" -- but no such explanations for why one might misinform.) And no doubt there are yet others.
But I think a major part of it has to be that ignorance heals better than confusion when placed in a bigger pool of evidence. Do you agree? Do you think "lies" are worse than "secrets", and if so, why?
I think we inherit this idea of "lies are worse than secrets" from classic deontological morality (an act-utilitarian could try to quantify the harm caused by each and compare, so he doesn't have as deep a problem)
In my opinion, a lot of deontological morality is rooted in a system for minimizing blame The guy who wouldn't push the fat man onto the tracks to save the people in the trolley problem ( http://en.wikipedia.org/wiki/Trolley_problem#The_fat_man ) knows that he couldn't be blamed for the trolley victims' death, but he could and would be blamed for the murder of the fat man. Therefore, he concludes that leaving the people on the track to die is more moral. Now, looking at your analogy:
"If a man is starving, not giving him a loaf of bread is as deadly as giving him cyanide. But if there are a lot of random objects lying around in the neighborhood, the former deed is less deadly: it's far more likely that one of the random objects is a loaf of bread than that it is an antidote to cyanide."
If I give a man cyanide, then I am clearly and visibly to blame for his death. From a status point of view, that's social suicide. If I fail to give him a loaf of bread, society isn't going to come knocking down my door to drag me to jail. For one thing, no one will even associate his death with me. For another, everyone else who didn't give him bread will be equally to blame. Therefore in classical morality, giving him cyanide is an evil act and not giving him bread is a neutral or barely-evil act.
Now apply that to the lies versus secrets question. If I tell a lie, and I'm caught, then people have every right to get mad at me. If I don't tell you some information that is necessary for you to succeed, you can never prove that I did it intentionally and everyone else who failed to give you that information is equally guilty. Therefore classical morality considers lying worse than keeping secrets, even in cases where utilitarian morality says I've harmed you exactly the same amount either way.
If we alter the situation to make it easier to pin the blame on me, classical morality starts condemning me more. If I am the sole witness in an important criminal case and I describe the entire scene accurately except that I fail to mention I saw the suspect there with a knife, and then a videotape later shows me at the scene, staring at the suspect, I will get in trouble. In this case, it's easy to blame me for not conveying the information, since I was ritually placed in a position where conveying the information was my sole responsibility and since it can be proven I withheld the information intentionally. And in this situation, most people would consider my withholding of information "immoral".
"If I fail to give him a loaf of bread, society isn't going to come knocking down my door to drag me to jail."
Unfortunately this is not entirely correct. Some hold the social principal that "positive rights" would socially demand such actions and in many circles withholding said loaf of bread would be equivocated to cyanide poisoning.