No. It's nonsense to say that it's NEVER valid.
There's a fad, among Republicans to prove Republicans are dumber than we are, by denying that fascism is "Right wing". That's the main problem, these days.
There's one huge difference between Trump and Hitler. Hitler killed millions. There are MANY similarities, but all of them, together, do not equal that huge difference. For example. Hitler put Goebbels in high office. Trump did the same with Bannon. In both cases, smart people were STUNNED at the transparency of putting a known liar in high office, just so they could deceive stupid people. That's both Trump's and Hitler's specialty.