Why is Atheism such a poor evolutionary strategy

One of the things that I've always wondered about the 'rationalist' (aka atheist) community is why in evolutionary terms it is so poorly selected.  Religious people have far more kids than the 'rational' and us religious nutters don't even believe in meta-evolution.

If rational atheism is so right and accurate, why does it turn out to be such a lousy reproductive strategy?  

Is God hating a turn off?  Does belief in one's pending existential obliteration lower sperm counts?

Or is contempt for God simply correlated with contempt for children?

In other words, what is the rationalist argument for evolutionary irrationality?