[einarfd]

So where is the slippery slope in the Martin Niemöller poem?

The transgression against the groups does not change, it is just repeated on different "troublesome" out groups. I guess you can argue that the last line, where the I of the text is taken, is the slippery slope. But that seems a bit contrived.

My reading of it is that it is an admonishing against accepting injustice against groups that you yourself is not part of, and that if you do not speak up. Then who will speak up for you, if you need it.