It's a very common tactic of apologists and defenders of a faith to point out that atheist governments has killed large numbers of people.

Very often this argument comes across as a very soft tu quoque fallacy, or a, "yeah well so do you." It's ironic then that so many of the examples used run counter to the narrative, Hitler was a confirmed catholic and even if his personal beliefs were unorthodox, the majority of Germans were Protestant and Catholics who had been primed with anti-semi toms for years.

The soviets had a long history of orthodox Christianity and the number of churches under Stalin actually grew rather than shrank. Stalin even went to seminary.

Even the Asian nations were religious to a degree, Buddhism and Taoism while more atheistic can and often are theistic in practice, or at the very least include supernatural overtures.

Let's also not forget that while America is a secular nation the president that ordered, and the bombers that dropped atomic bombs were most likely Christians.

The point is that as humans we are capable of extreme barbarism and acts of violence, regardless of whether we believe in supernatural special pleadings or not.

It's also important to recognize that while atheism is central to Marxism and Commnism, not all atheists are Marxists or Communists, which is the one thing Stalin, Mao, and Pol Pot had in common. This isn't to say all Communists or Marxists are murderers but to point out that like other ideologies and like religions adherents to rigid ways of thinking are very happy to kill the unbelievers.

So it's hardly true that we atheists are better at killing, and more apt to say that simply being an atheist is not sufficient to make one a better person or less subject to violent ideologies and tribal mentalities that lead to violence.