Two of the states you alluded to substituted a divine entity for the state itself; the state itself was God. The idea that those states committed horrific atrocities because of atheism is a straw man.

Show me a state that has cast off religion, cast off totalitarianism, and led by the principles of the enlightenment, of Jefferson, of Paine, and still committed atrocities, then you might have an argument. But as it is, your argument falls flat.

BTW... Hitler made extensive reference in Mein Kampf of "doing God's work" by expelling the Jews from Germany. The first treaty reached by the Third Reich with another sovereign state was with the Vatican, just six months after Hitler became Chancellor. And "Gott Mit Uns" ("God With Us") was part of the Wermacht uniform. (It was engraved on a belt buckle.)

I could go on...