We don't want another Holocaust or Gulag camps here ever again. I'm fine with restricting some speech. It's a small price to pay.
I see all these arguments waxing poetic about how dangerous it is to... I don't know, give anyone power? As if we haven't had these debates before. We have concrete examples of policies and behaviors that are harmful on fascist/Communist (big C is important) levels. We can compare someone's rhetoric and actions to those of people who have done the kinds of harm we want to prevent. We can use reasoning to parse their arguments instead of reacting emotionally. People do this every single day.
If it's really your concern that we can't define what dangerous ideologies are, then educate yourself, because we can.
It's very difficult because calling someone "Nazi" means you get to attack the "Nazi". So people who want to attack others just call them Nazis to justify it.
It's happened a lot in US politics, but for an example everyone here can agree on, "Ukraine is infested by Nazis" was one of the excuses for Russia invading Ukraine.
Yeah, that's not true. That isn't something that happens.
I'd be surprised if you can find even one news article about a non-fascist being called a Nazi and then attacked and everyone being ok with it. Nazis don't get punched as often as they should.
Russia invading Ukraine is not a good example. Much of the rest of the world said "No, you're full of shit and we're sending Ukraine missiles." I don't think anybody has actually supported Russia's "anti-Nazi" justification, even those countries economically bound to Russia and unwilling to resist them. It's just something Russia said, that doesn't mean it worked.
Further, international invasions are extremely different from internal politics are extremely different from personal/public interactions. You're painting broad strokes as if the entire planet of 8 billion people has the same mindset that "you can call anyone a Nazi and attack them." That doesn't even make sense. We are talking about US culture.
Finally, I shouldn't even be replying since it doesn't seem you read the majority of my previous comment. I've already said this: we know what Nazis are. You can call anybody anything, but whether or not they're a Nazi depends on if they hold Nazi beliefs.