MrHen left LessWrong believing in a God, and Mitchell_Porter (as far as I can tell) still believes dualism needs to be true if colour exists (or whatever his argument was, I'm embarrasing myself by trying to simplify it when I had a poor understanding of what he was trying to say). They were/are also great rationalists apart from that, and they both make sure to be very humble in general while on the site.

Compartmentalization.

Bold statment that somehow still seems true: Most LessWrongers probably have a belief of comparable wrongness. MrHen is just unlucky.