Appropriate use of history

For quite some time I have been thinking about this so tell me your thoughts. It seems names and insults sometimes take historical events and use them.

Examples (there are more tactless ones but I’m not gonna include them for obvious reasons - I think we’ve all heard some of them tho):

“You’re such a Hitler”: someone who’s very strict and set in their relentless ways.

“Feminazi”: “feminists” who are not supporting equality but misandry in sometimes aggressive ways

“Grammar Nazi”: Same only with the correct use of grammar

In my country it’s also common to just call someone a Nazi if they are leaning towards the “right wing” (we don’t really have just two wings but for easier understanding, hence the quotations marks) and you don’t agree with their views on things.

And some who were pointed out by me and are not really just mentioning historical events but are along the same lines:

“You’re wearing so much white you could be a Klan member”

“If you keep doing x we’ll have to call the KKK”

Now my question is, do you see some/all/none of them as appropriate or rather not inappropriate and why? In what way could they be used without being offensive if there is such a way? And why, in your opinion, have the Nazis specifically become such a commonly used synonym for a lot of things when what they did was a huge crime against humanity?

Curious to hear your opinions!

Also, if there are similar phrases you know of regarding other historical events please share.