If someone was being harassed and censored because they were accused of being a flarndingle, I would have a problem with that. If corporate America were calling for mass censorship of "flarndingle" literature, I would be opposed to that.
I would not like being called a flarndingle if I knew it would mean that I would be censored. It does not matter that flarndingle is a meaningless word.
The term neo-nazi is actually quite abstract. For many younger people and activists, it has just become a synonym for "person I do not agree with".
It has become a catch-all insult that can be applied to anyone. There is nobody who that insult won't stick to. You can be a Jewish academic with controversial opinions about society and have "anti-fascist" activists target you for being a neo-nazi.
So, obviously we can't ban anyone that is called a neo-nazi.
Yes, the term "neo-nazi" is sometimes misapplied. That misapplication doesn't mean that neo-nazis don't exist, or that the term has no meaning. If the term didn't have an established, commonly agreed upon meaning that referred to a specific ideology and movement in the real world, then there would be no reason to quibble about its misuse, because calling someone a neo-nazi would be as meaningless as calling them a flarndingle.