There is a column in the Christian Science Monitor which has as its premise that "Atheism, not religion, is the real force behind the mass murders of history". And then it goes off about how most of the religious based killing in the past has been minor compared to the damage done by modern "atheists". And some of what the columnist says is pertinent. However, towards the end of the column, he shoots himself in the foot with this statement: "...cannot explain why, if Nazism was directly descended from medieval Christianity, medieval Christianity did not produce a Hitler."
Well, the short answer is that the rise of Hitler required the technology of the 20th Century. Also, while Hitler's motives were complex, his antisemitism was, in fact, a direct result of centuries of religious persecution. The deaths of over six million Jews can be laid directly at the feet of religious intolerance. Nope, sorry...Harris, Dawkins et al have a point which needs to be considered.