Godwin's law (also known as Godwin's Rule of Nazi Analogies or Godwin's Law of Nazi Analogies) is a humorous observation made by Mike Godwin in 1990 that has become an Internet adage. It states: "As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1."
And when the Nazi card does get played, as it is played early and often against atheists, "evolutionists" and "Darwinists," my reaction is usually something like: This needs music. If you are going to parade the Nazis in front of me, let's give them something to dance to.
For a damn fine takedown of the idea, often claimed by religious yo-yos of all stripes, that Hitler and his Nazi buddies were atheists or "Darwinists" or supported the concept of common descent, go here.
I did have one tiny disagreement with the author, however; my understanding is that while Mein Kampf sold enough copies to make Hitler fairly wealthy, and was often given as a wedding or graduation present, no one actually read the damn thing. Not even the most devout Nazis could get through that turgid pile of crap. Hell, I own a copy, and I've certainly never read it; not all the way through, anyway, or anything even close to it. I sometimes check citations I run across reading online, but I am not likely to hazard an actual reading of the thing. It really is quite unreadable, and for so many reasons.