You know, despite the fact that that poem is about the Nazis, it does have a point beyond that. I've mostly seen it referenced as "be aware of these kind of issues, it could be you next", rather than "<issue> is just like what the Nazis did!" To say that this is a case of Godwin's law misses the point: it is a good idea to be active in calling out injustice even if you are not personally affected, because one day you could be. It does not always warrant the gravitas of comparing it to the Holocaust, but the poem itself is a nice succinct illustration of the idea that preventing injustice against others is a wise idea.

Also, calling Godwin's law on a legitimate comparison is just as bad as what Hitler did. :-P