“Nazi”, a metaphorical word?

Why do so many people use the word “nazi” metaphorically? This word has a very specific meaning in a very specific historical context. I think it’s dangerous to use it beyond its proper meaning.

There will be a time when all the victims and close parents of victims of the holocaust will have died out, and when the word “nazi” doesn’t really mean anything any more. When that time comes, everything will be ready for the world to see real nazis appear again, in whatever form will be most likely at that time.

This word is one of the few things that are left to remember what was probably the greatest tragedy of History (I think I am objective in saying that, my education, family and background being completely a-religious), I would love to see it stay intact.