(Ideas below are still works in progress, listed in descending order of potential disagreement:)
Bearing children is immoral. Eliezer has stated that he is not adult enough to have children, but I wonder if we will ever be adult enough, including in a post-singularity environment.
The second idea probably isn't as controversial: early suicide (outside of any moral dilemma, battlefield, euthanasia situation, etc.) is in some cases rational and moral. Combined with cryonics, it is the only sensible option for, e.g., senile dementia patients. But this group can be expanded, even without cryonics.
Some have mentioned modern school systems to be broken, but I'll go even further and say that mandatory education is a huge waste of time and money, for all involved. Many, perhaps most, need to know only basic literacy and arithmetic. The rest should be taught on a want-to-know basis or similar. As a corollary, I don't think many or even most people can be brought into the fold of science or rationality.
(Curiously, the original poster wondered if our crazy beliefs might be true, but many responses, including my own, are value, not fact, judgments.)
What do you believe that most people on this site don't?
I'm especially looking for things that you wouldn't even mention if someone wasn't explicitly asking for them. Stuff you're not even comfortable writing under your own name. Making a one-shot account here is very easy, go ahead and do that if you don't want to tarnish your image.
I think a big problem with a "community" dedicated to being less wrong is that it will make people more concerned about APPEARING less wrong. The biggest part of my intellectual journey so far has been the acquisition of new and startling knowledge, and that knowledge doesn't seem likely to turn up here in the conditions that currently exist.
So please, tell me the crazy things you're otherwise afraid to say. I want to know them, because they might be true.