Thought of a few more:
Circumcision may be harmful, and may cause more harm than benefit.
It's generally not worth your time to ask a doctor questions about treatments; the responses you'll get will be soothing but non-informative.
Doctors probably cause more harm than good, considered over all interventions.
Annoyance, do you intend the last sentence to broadly mean "treatment is less effective than prevention," or "Western medicine is a crock," or "Doctors specifically are not as effective as other aspects of modern medicine," or something else?
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.