Godwin’s Law seems to be interpreted differently by different people. It’s original meaning is different than how I usually see it interpreted. In its original form it says:
As a Usenet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.
Note that its original meaning makes no value judgment as to the appropriateness of the comparison with Nazis – only that such a comparison becomes highly likely as the thread grows longer. Whether the likelihood actually approaches one or not is debatable, but it isn’t important. The “law” was originally just meant as a kind of humorous quip.
Anyhow, the definition at the above link continues:
There is a tradition in many groups that, once this occurs, that thread is over, and whoever mentioned the Nazis has automatically lost whatever argument was in progress… More precisely, the subsequent value of the thread is zero.
That is the definition that I have most often seen thrown around – in a serious manner, as if such a law was actually an immutable fact of nature. People have occasionally thrown it at me when I’ve pointed to analogies with Nazis, claiming immediate victory in their argument with me. That is the definition that I want to address here.