In What's So Great about Christianity, Dinesh D'Souza claims that one of the psychological reasons why people adopt atheism is because they are very sexual and most traditional religions put heavy restraints on sexual behavior. Who wants to believe in all those rules when you have the libido of a bonobo?
I looked at infidelity to see if there was a relationship between skepticism and deviant sexual behavior. The table shows that there clearly is. As skepticism grows, so does the risk of cheating. Compared to believers, all categories except "believes sometimes" have significantly higher rates. Atheists are almost twice as likely to stray. (This finding is also consistent with the greater sexual deviance and skepticism seen among men).
Of course, this link does not identify what is causing what.