I have heard it claimed many times that Stalin and Mao killed people in the name of atheism, which frankly is not true. This is usually brought up as a counter-example to when someone criticising religion brings up the issue of killing in the name of god(s), which there are countless examples of. I'll try to briefly explain why Stalin and Mao did not kill in the name of atheism.
Neither of these dictators were motivated by atheism to commit their atrocities, rather they were motivated by their twisted communist ideologies. Anyone who opposed their rule was hastily silenced (read: murdered). It is as simple as that. To quote Richard Dawkins, "There is no logical pathway between atheism and killing people".
This is why attempts by theists to return the shit-slinging will always fail. There is an obvious pathway between many different religions and violence. Take Islam for example, its founder Mohammed was a tyrant, who went around the middle east killing people who didn't convert to Islam. On top of that, there are many passages in the Qu'ran that say things along the lines of 'kill infidels'.