Eh, Nazi Germany wasn't atheist. USSR, PRC and Cambodia definitely were, but Nazi Germany literally had many clerical supporters.You are right in some respects, but the level of sadism required to exterminate a whole ethnic group is thankfully extremely high. Another thing to consider is that all mass murdering regimes of the 20C were officially atheist regimes(Nazi Germany, USSR, PRC, Cambodia etc.) I have a hard time imagining a superstitious russian muzhik(the Vozhd's presumed support base?) mannin camps where they funnel human beings to their death. What I'm saying is that Nazism, or Communism can in certain circumstances justify mass death, but Christianity never can, nor Islam etc etc. I dont know maybe Im wrong but thats my thoughts.