Godwin's law

Godwin's law is a humorous eponymous law formulated by Mike Godwin in 1990, which states that:

"As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1."

The law is an observation that, as Internet discussions can become more heated over time, the longer the discussion the likelihood is increased that one of the arguers will compare either another arguer to a Nazi or Hitler directly, or their viewpoint as having a Nazi- or Hitler-related component. This appears to be especially true during any discussion of atheism with religious people.