This one started with the idea that religions have an expiration date. There were a lot of religions before Christianity took hold of the world, some of them really really old. The innovation of both Christianity and Islam is that they introduced prophets, new versions of their Gods and proof that they are not dead, uncaring or otherwise absentee. So, I asked myself, is it possible that a religion has an expiration date, after which it can't support the hold on its followers and they drift away to other things, like Scientology?
Then, the second idea. In order to create a new religion, one that can be called something more than a sect, we need a prophet. Someone with a history so outrageous that people can associate it with divinity. He or she must also sacrifice themselves for their strict ideals and/or people. We also need someone who came about sooner than 2000 years.
Idea number three: Hitler! He affected the entire world, he had pretty strict ideals and has sacrificed himself for them and (presumably) for his people, whoever they might have been. Outrageous life: check. New to the scene: check. Fanatic following: check. He is the perfect prophet! Add to this his deep hatred of Jews, who can only be reasonably differentiated from other people only by their religion. Add to this the mysticism that consumed Hitler before he died and his fascination with the occult. You get a prophet that burned the world for religious reasons.
Idea number four: That idea number three must piss both sides equally much. Neonazis would probably consider it blasphemy (thus unwittingly giving strength to it). Jews... well, they are pretty pissed at Nazis. Any cult based on them would probably disagree with them, too. The other people, they would bring into the argument the horror of war and the Holocaust and other things like that. Admittedly, the God that Hitler would have been a prophet for has to be pretty twisted, but we've seen worse, as gods go. The present ones are Gandhi compared with the old bunch.
Idea number five: we've discussed a ridiculous idea and the arguments against it are pretty much liked to the horror that Hitler brought onto the world. While over 70 million people have died as a consequence of World War II, we fixate on the religious connotations of the Holocaust and the directed persecution of one people. I hope I am wrong, but when I imagine the angry masses, terrified by this idea of mine, I imagine people bringing the Jew massacre in the forefront, with pancards and signs with "Never again". And that leads me to this fifth idea: that if 6 million people being massacred for their religion and nationality is horror, then the rest of 64 million being ignored or considered casualties of "regular" war, the idea that people can be killed in the millions and it is OK, if there are political and economic reasons for it... that is true horror.