The simple truth is that people who are willing to denounce logical reasoning in favor of faith are more likely to accept genocide than people who are skeptical of religion.
If this is the truth then how do you explain Lenin's, Stalin's, Pol Pot's and Mao Tse Tung's policies?
It seems that atheism comes in as many variants as does religion (from a thinking Catholic's perspective):
http://www.carl-olson.com/articles/atheism_envoy.html