Nazis seek to silence others through violence or threats of violence.
If you believe in freedom.of speech you should seek to protect these minority voices that are being silenced by violence, you shouldn't be protecting people making death threats.
But the problem is saying that Nazis, without violence and threats of violence can silenced. And if you silenced people even before the threats, how can you say you're for the freedom of speech?
Humans can become monsters.
Nazism and fascism metastasize in open societies. If they have a forum, if they're allowed to congregate online or in real life, they self-radicalize.
I'm extremely pro-free-speech, often to a fault -- but that doesn't apply to actual Nazis or other people who promote hate and violence.
This is really toxic shit and can be impossible to control once it gets going.