This is a pretty long response, so my apologies that I'm not addressing every part of it: I used to do that in Internet conversations but it gets untenably long pretty rapidly.

> I don't think that it's enough to stick with such post-Enlightenment ideas if it means defending the right for people who advocate genocide to speak.

As I mentioned, I'm comfortable with drawing the line at calls to violence, and the Daily Stormer's "gas all kikes" certainly qualified on its face. Do you also feel the same way about "kill all men", "kill all whites", "die cis scum", etc? Do you think that all domain registrars should be blacklisting Twitter, which condones far higher volumes of sentiments that are exactly as violent, and hide behind the same exact justification of unserious provocation? If you do, then you're to be commended for your intellectual integrity, but know that you stand more or less alone in your consistency. If, like everyone else calling for legal speech to be no-platformed, you have an unprincipled exception for those whose politics are more aligned with yours, then pretending that you firmly stand against "calls to genocide" even when the callers claim they're joking is just a fig leaf for shutting down speech that you dislike.

> They would be if they truly existed, but they exist only in the mind of their proponents and almost nobody else.

Did you just assert that the concept of an open marketplace of ideas can't exist, without bothering to justify this extraordinary claim? What a bizarrely fart-in-the-elevator approach to discourse. The fact that a pure, ideal free marketplace of ideas doesn't exist couldn't be less relevant to the concept that we should aim towards it anyway.

> I disagree, for me important views almost wholly contain the pursuit of justice and the elimination of unjust hierarchy - something which can be pursued without letting Nazis have their say.

And this is exactly my point. People pretending to be high-minded and just, but the minute you poke at their philosophy, it comes down to the arrogance of assuming that their worldview is so much more correct than everyone else's that they don't even need to hear anyone else. As I said, literally everyone in history thought they were the good guys, and it was only until we figured out techniques for coexistence between differing ideas of goodness that we stopped murdering each other every time a new POV gained political power.

Marcuse is falling prey to exactly the same thing I'm describing above (and was frankly kind of an idiot). The medieval Catholic Church, any number of Islamic terrorist orgs, Stalinism, the Nazis: all of them had high-minded descriptions of why those who didn't share in their ideology weren't worthy of the privilege of expressing their ideas openly. Given that they assumed their values were just as correct as you assume you are, their explanations were just as compelling.

There's a reason the European wars of religion were among the bloodiest in history: when your opponent isn't even present inside the personal moral framework you're too blind to see outside of, they're unpersons that you can do whatever you want to. Just because you can't see out of your tiny, narrow view of world doesn't mean that everyone else is similarly blind: more people like you terrify me a hell of a lot more than neo-Nazis currently do. People aren't born neo-Nazis, and marginalizing everyone to the right of you as not part of civilization is only going to swell their ranks.