Well this was an interesting read:
"First, Goodwin’s law. In its original form, it stated that as a usenet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one. One evolution is that it is now applied not to usenet discussions (of blessed memory) but, first, to all internet discussions, and then to debate in general. And another evolution is the qualification that, once the comparison occurs, the debate is automatically ended and whoever made the comparison has automatically lost."
cearta.ie -> Three internet tropes