I have seen on various Atheism forums trolls that look to the deaths that can be laid at the feet of Stalin and Mao as proof that Atheism is inherently immoral and capable of worse atrocities than Theism ever could be. People play the numbers game with it. Yes, millions more died in a shorter period than ever. They ignore the fact that this happened because: a) there were significantly more to die and b) our capability to kill by design or accident (the latter category being the larger one in both men’s cases due to insane and egotistical economic and industrial policies) was greatly improved.
These people who make this argument about those two “Atheists” miss several points. First, playing strictly the numbers game again, they ignore all religious murder after Uncle Joe came along. So Hitler (yes he was a religious fanatic among other things), the Islamic extremists, and hyper Zionists in Israel’s political right-wing all get a pass from them. If you don’t do that, suddenly you see more people have still died at the hands of religion, though frankly, that is irrelevant regardless of who has the higher “score.”
Second, atheism was not a driving factor for either man. Each used Marxism (ignoring subtler details like the need for a saturation of capital, something that didn’t occur in either country, before a true revolution of the proletariat could occur) as their inspiration. Rejection of the divine is only one small part of that.
Third, both men used Marxism, or Communism if you prefer, in the same manner that war and fear mongering religious leaders have used their holy texts over the years. They actively encouraged their people to not critically reflect on their own actions or their orders. They kept their followers too busy and too frightened to actually read the words of Marx, much as many Christian (other religions too, but the evidence is easier to present for these guys) leaders gloss over much of the New Testament that prohibits proselytizing or judgement. They actively hid the contradictions between their policies and the words of Marx, just as religious leaders do the contradictions in their holy texts.
Finally, and I know this one is a bit thinner but it is very important: neither man was truly an atheist. They each worshiped the cult of their own personality and actively encouraged others to do so. It was this, and Joe was very, very good at, that created, dare I say it, a religious fervor surrounding himself that encouraged people to harm others or themselves.
Blind belief, whether in an unknowable divine (Yahweh) or in a cult of personality (Mao), encourages action without reflection and eventually horror. Atheism rejects all belief, including the belief that any one individual is more important than the rest of us. Actually being an Atheist, and not just saying you are one, provides a degree of protection from being drawn into such horror. It does not insulate you entirely, I have known violent and crude Atheists. Nor does belonging to a religion automatically make you prone to blindly following the dictates from your Popes, clerics, monks or whoever. It does however open you up more to it, and history has borne that out and accusing Atheism of being responsible for these two men and their followers, who have more in common with religious fanaticism than they do Atheism, does not change that.