If you're constantly comparing people to some group, you can't talk about that group without being suspected of dogwhistles. Which forecloses discussions that otherwise could have been interesting.
It's also the insidiousness of Nazis. People always look at the holocaust and wonder how it could ever happen, and the answer as far as I can tell is Nazis weaponize the benefit of the doubt.
When you look back at how the world received Hitler before he became the Hitler we know, you see publications like the NYT musing that Hitler really doesn't mean anything he's saying about the Jews, and when he comes to power he will temper himself [1]:
So violent are Hitler’s fulminations against the Jews that a number of prominent Jewish citizens are reported to have sought safe asylums in the Bavarian highlands, easily reached by fast motor cars, whence they could hurry their women and children when forewarned of an anti-Semitic St. Bartholomew’s night.
But several reliable, well-informed sources confirmed the idea that Hitler’s anti-Semitism was not so genuine or violent as it sounded, and that he was merely using anti-Semitic propaganda as a bait to catch masses of followers and keep them aroused, enthusiastic, and in line for the time when his organization is perfected and sufficiently powerful to be employed effectively for political purposes.
Same thing is happening today. Trump is telling us he is going to genocide Gaza, he's going to create a concentration camp at Guantanamo Bay, annex Canada, invade Greenland, invade Mexico, cut out Congress, defy the Judiciary, serve past his constitutional term limit, and be dictator "for a day"... maybe let's just take him at his word instead of giving him the benefit of the doubt?
Sometimes the other group is neo nazis and are the dominant power.
Sometimes they are close enough but different that the similarities strike normal people. Except when they bring it up, the defense is “no actually the Nazis we’re specifically doing XYZ. This isn’t the same.
Which shuts down conversation about both - the actions being similar or identical.
If you're constantly comparing people to some group, you can't talk about that group without being suspected of dogwhistles. Which forecloses discussions that otherwise could have been interesting.