[Classic] "The Reagan Doctrine" by Isaac Asimov

"Some time ago, Ronald Reagan pointed out that one couldn't trust the Soviet government because the Soviets didn't believe in God or in an afterlife and therefore had no reason to behave honorably, but would be willing to lie and cheat and do all sorts of wicked things to aid their cause.

[...]

Yet there are puzzles. Consider Iran. The Iranians are a god-fearing people and believe in an afterlife, and this is certainly true of the mullahs and ayatollahs who comprise their government. And yet we are reluctant to trust them for some reason. President Reagan himself has referred to the Iranian leaders as "barbarians.""

Isaac Asimov, The Austin American-Statesman, May 10, 1981

A great read on the matter of "Why you can't trust Theists" I mean "Atheists".