This happens as time passes and events slip in societies memories. There are increasingly fewer and fewer people who were around to witness the atrocities of the Nazi rule, and even the people who knew of it second-hand are slowly disappearing. There's two groups of people who use the word Nazi and Hitler to insult someone; the first group is full of idiots who should know better and the second group is full of people who were completely unaffected by the history in any way, meaningful or not.

People compare societies to Rome all the time, saying America or the western world is akin to the downfall of Rome, seemingly oblivious to the atrocities committed by various tribes ransacking the Empire. Not that I agree with comparisons to Hitler or Nazis, I think they're arguments of a weak mind, but history was a long time ago.