For good people to do evil doesn't require only religion, or even any religion, but simply one of it's key elements: belief without evidence-in other words, faith.
And that kind of faith is seen not just in religion, but any authoritarian ideology that puts dogma above truth and frowns on dissent.
This was precisely the case in the totalitarian regimes of Maoist China and Stalinist Russia, whose excesses are often (and wrongly) blamed on atheism.

Jerry A. Coyne