Godwin's Law of Nazi Analogies: As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.
There are also a number of corollaries:
Libertarianism (pro, con, and internal faction fights) is the primordial netnews discussion topic. Anytime the debate shifts somewhere else, it must eventually return to this fuel source.
As soon as such a comparison occurs, someone will start a Nazi-discussion spinoff thread on alt.censorship.
If the USENET discussion touches on homosexuality or Heinlein, Nazis or Hitler are mentioned within three days.
As global connectivity improves, the probability of actual Nazis being on the net approaches one.
As a network evolves, the number of Nazi comparisons not forestalled by citation to Godwin's Law converges to zero."
Godwin's Law doesn't actually close down threads ... there is a corollary, not quoted at the source below, which roughly states that the invocation of Nazi/Hitler reduces the information content of the thread to zero.
See also EFF page on Godwin's Law