Outside of Communism/Marxism (which is completely incompatible with human nature) what atrocities have atheists been responsible for?
Abortion?
That's an interesting question, and one which I'd like to take seriously.
Correct me all along here if I'm wrong, because I'm struggling even to get the conceptual framework in place here:
Before Voltaire and his crew the late 18th century, I don't think there were people in Europe or America who would have called themselves "atheists," a term which would have been used only as a denunciatory label applied to an opponent, meaning either "morally bad" or "heretical." And I don't think there was anything like open, organized atheism until the French Revolution.
So you're dealing with a phenomenon which has only been a force in history for less than 250 years; unlike, say, the Judeo-Christian movement which has 2500+ years' worth of history to poke around in looking for vice and virtue.
OK, so looking at the movements or parties which represented atheists' ideals and aspirations since they got out of the salons and into the historic cavalcade, you've got:
It looks like --- other than Nietzsche and Ayn Rand --- a pretty Left-wing line-up.
Now, I don't want to blame atheists unfairly for everything from the Reign of Terror to the British CND, but those are the only organized movements of atheists I see on the world stage.
In all sincerity, I ask: if we are not to judge atheism by its organized historic manifestations, how are we to judge it?