We think that religions are false, and a shared priority of Less Wrong denizens is to >believe things that are true instead

You'll get no argument from me that religions are false. You will get practically no argument from me that it makes sense to want to believe things that are true. What I question is, is it always rational to make others believe things that are true? If I leave my lights on when I leave the house so that would-be robbers think I am home when I am not, I am making a rational decision to make others believe something that is false.

If I am playing the Prisoner's Dilemma with someone (just once, so no tit-for-tat or anything), and I have the choice of making my opponent either act rationally or irrationally, the rational thing for me to do is make him act irrationally.