Ad Hitlerum arguments are arguments by analogy — you criticize your opponent's views or proposals on the basis of their similarities either to those of Nazi Germany or Hitler himself.  And so: Vegetarianism? No way — many Nazis were vegetarians.  Or: The Nazis favored euthanasia, so it must be wrong.  The crucial thing for these arguments is that Nazis or Hitler favoring X means that X is morally unacceptable.  But this is a pretty unreliable method of detecting immorality, as the Nazis also were avid promoters of physical fitness, environmentalism, and classical music.  So ad Hitlerum arguments regularly suffer from problems of relevance.  But that failing of the argument hardly ever prevents folks from using it. Regularly.

Godwin's law, one of the oldest of the eponymous Laws of the Internet, runs that: "As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1."   Given that the argumentative strategy has regular relevance problems, there's a widely recognized corollary to the law, which is that whoever makes use of the argumentative strategy has thereby lost the argument.  It's in the same boat with appeals to the subjectivity of an issue, after having had a heated argument about it.  It is an argument that is a last-ditch grasp at straws.

So far, none of this is news.

Here's the news: Hal Colebatch, in  his post "Don't Be Scared of Goodwin's So-Called Law" at the American Spectator, is urging conservatives not to be deterred by the charge of "Goodwin's Law."  The law of the internet, instead of being used as a tool for improving discourse, has hampered good argument. He writes:

Try mentioning to a euthanasia advocate that the Nazi extermination program started off as an exercise in medical euthanasia. And as for suggesting that Jews and Israel are in danger of a second holocaust if Muslim extremists have their way, just wait for: "Godwin's Law!" "Godwin's law!" repeated with a kind of witless assumption of superiority reminiscent of school playground chants.

The first question is: with whom has Colebatch been arguing?  Nobody, at least nobody serious, in any of these debates does that chanting stuff. (I smell weak-manning here.) The second question is why would anyone serious about the issues even be bothered by this response?  His article urges people not to be "afraid" of Goodwin's law — who is afraid of people arguing like that?

Colebatch, first, seems to think that the counter-argument is in the chanting.  Or maybe in the thought that someone's lost the argument.  But the real point of noting Godwin's law in a discussion with someone who's just made an Ad Hitlerum move is to challenge the aptness of the analogy.  So take Colebatch's own example — wouldn't the point of bringing up Godwin's Law there be to say something like: euthanasia programs aren't out to do anything more than allow some people to die with dignity.  It's not a cover for something else, and there are oversight programs to ensure that it doesn't turn into something else.  Unless it's shown that there are other plans for euthanasia, there's no relevance to the analogy.

So Colebatch is not being silenced or intimidated when someone says "Godwin's Law" to him — he's on the receiving end of a rebuttal.  But he can't recognize that:

Personally, I don't intend to be intimidated by chants of "Godwin's Law" or any other infantile slogan, used to smother debate in a way reminiscent of something from George Orwell or, if you'll excuse me saying so, a Nuremberg Rally. I have come up against echoes of Nazi thought-patterns and arguments many times and not only am I not going to be bullied into keeping silent about this, I believe every civilized person has a positive duty to speak up about it whenever appropriate.

But Godwin's Law isn't smothering debate at all.  It's a move to point out a fallacy.  Or at least a challenge to demonstrate relevance.  Since when is criticism of an analogy a form of intimidation or something infantile?  That's what good debate is about!