Niemoller’s pro-Hitler, pro-Nazi stance is properly noted by posters in this thread (and another one.) A few things to add. He was imprisoned in concentration camps, including Dachau, for 7 years. He admitted his culpability and grievous errors, and tried to make amends. He purposely chose to identify Communists, socialists, trade unionists, and Jews in his speech because as he admitted, he and many in his church, community, and social circles had not cared about “those people” at the time. Thus it is in part an ongoing confession of his own terrible failing.
Not arguing for forgiveness here.
Finally, whatever its provenance, the warning is an important one. Thanks, @Smapti, for the updated version!