It seems that the examples given in the article are about non-US citizens caught in a tangle of sorts but some physicists are wanting to apply it to themselves as a whole.
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""First They Came" (German: Als sie kamen lit. 'When they came', or Habe ich geschwiegen lit. 'I did not speak out'), is the poetic form of a 1946 post-war confessional prose piece by the German Lutheran pastor Martin Niemöller (1892–1984). It is about the silent complicity of German intellectuals and clergy following the Nazis' rise to power and subsequent incremental purging of their chosen targets. Many variations and adaptations in the spirit of the original have been published in the English language. "
When you see things happening to those outside your circle you might feel safe, but many times you are just further down the list and your time will come.
"A slippery slope fallacy occurs when someone claims that a position or decision will lead to a series of unintended negative consequences. These negative consequences are often bad and/or increasingly outlandish. The person using the slippery slope fallacy takes these consequences as a certainty and does not analyze the logic of their own position. A slippery slope fallacy can be used as a deflection to avoid discussing the merits of a position, shifting the field of debate."
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.