If the results of such reflection adds to the utter dedication to ensuring nothing even approaching The Holocaust ever happens again it is I believe a worthwhile exercise
To me the answer is very simple and straightforward. The greatest mass murders in history took place under the regime's of communist and fascist dictatorships. These had one over riding thing in common the leaders were atheists. Even though Hitler and Himmler were raised in a Catholic household they were atavistic ideologues with no Christian ethics.
Pol Pot, Stalin and Mao were outright atheistic communists, and between them ended the lives of untold multi-millions. Pol Pot, on a per head of population basis was probably the worst of these monsters who were idealised by the "useful idiots" on the left in the West, especially in Europe. The North Korean leadership which has allowed mass starvation for countless numbers possibly runs Pol Pot a close second on a population basis.
It can be rightly stated that multitudes have been put to death in the name of religion but even with the most fanatical episodes of the Muslim advance out of Arabia to conquest of much of the world, or with the Inquisition at its height the option was conversion or death.
With the atheists it was simply death for all those who opposed them (whether genuinely or through the eyes of paranoia). At its very core religion, the undistorted religion of belief and submission to a supreme being and the ethical nature of that being, is life enhancing.
Atheism, which throws itself back on a humanistic animal mind has led to mass murder,a perfectly logical end result, and there is nothing I can see which would prevent an atheistic dictatorship from doing so again.