And one of the concerns I detected in wedrifid's comment (one I share myself) is that if highly intelligent and productive people start doing what obviously incorrect beliefs indicate they should, the world is going to be optimised in a direction I won't like.

Exactly! If beliefs like this are just used as verbal symbols for navigating the social world they do relatively minor harm. Once someone with the intelligence, productivity and otherwise rational thinking necessary comes to follow the belief to the logical conclusion comes along things start exploding. Or rationalist communities become modified in a direction that makes them either less pleasant or less effective than I would prefer.