Because if you drive people underground and further away from society you make them martyrs, and further radicalize their ideas.

This why I think something like the anti-Holocaust denial laws in Germany are stupid, all you need to do is listen to one of them and you'll see how little credibility they have, now if you run them underground you give them credibility, more than they ever could get by talking to them.

1. What constitutes a neo-nazi? Fascist and Neo-nazi has pretty much been redefine via persuasive redefinition as somebody we disagree with. People don't even use the word Fascism correctly anymore.

Redefined Fascism - Racist and authoritharian movement.

Actual Fascism - A 1 Centralized 1 party system with a strong leader, traditionalist values and nationalist leanings.

As to any political system there are pros and cons to fascism, believe it or not, and in certain circumstances it can make the country thrive, but on the other hand it has many other negatives as well, for one fascism is very good at mobilizing the people and stabilizing the country after years of strife and disrepair, Fascism didn't do too much of a bad job of stabilizing Spain after its civil war.

Caesar and Augustus' Rome was in many ways akin to a modern fascist state.

Now, that we've cleared up that people aren't even using the word fascist and neo-nazi anymore because they've been redefined to simply mean, somebody I dislike, let's move on;

1. The reason for the polarization of politics is the attitude of people who wish to silence others, be it the authoritharian right, or be it authoritharian leftists, if you truly want to solve this problem, banning and calling out people who disagree with you will solve shit.

2. In the battleground of ideas, the better idea should win, this however does not hold true when you don't actually engage with your political opponent, and rather demonize them and run them and their followers away even further where they can radicalize themselves, be it Nazi Germany, be it Soviet Russia, this happens over and over again and people keep doing it.

TLDR: We can't even decide on what being a fascist or a neo-nazi is since we use these words so sparingly, it would be very convenient to start just lumping everyone into the category of neo-nazi white supremacist, once their right of free speech is taken away.