“As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches” that is, if an online discussion (regardless of topic or scope) goes on long enough, sooner or later someone will compare someone or something to Adolf Hitler or his deeds, the point at which effectively the discussion or thread often ends.
Godwin’s law itself can be abused as a distraction, diversion or even as censorship, fallaciously miscasting an opponent’s argument as hyperbole when the comparisons made by the argument are actually appropriate. Similar criticisms of the “law” (or “at least the distorted version which purports to prohibit all comparisons to German crimes”) have been made by the American lawyer, journalist, and author Glenn Greenwald.
Godwin’s law does not claim to articulate a fallacy; it is instead framed as a memetic tool to reduce the incidence of inappropriate hyperbolic comparisons. “Although deliberately framed as if it were a law of nature or of mathematics,” Godwin wrote, “its purpose has always been rhetorical and pedagogical: I wanted folks who glibly compared someone else to Hitler to think a bit harder about the Holocaust.”