I still fear your position is leaving a loop hole open for nazis.

The free speech loophole has to be left open for everybody. The moment we let someone arbitrate speech, we no longer have free speech.

We don't need to let nazis to empower themselves to guard against groupthink.

A right for everyone has to be a right for everyone. If you study what happened in the rise of Fascism in the Weimar Republic, you'll find that it was the left leaning Weimar Republic that put into place the legal framework for Nazi totalitarianism. In almost every law that had to do with human rights, the Weimar Republic put in a "unless necessary for the public good" or "unless a law is passed to the contrary" clause. All the Nazis had to do was to use those clauses.

Free Speech protects society as a whole against groupthink. Any minority, no matter how small or unpopular, is protected. The moment you introduce Weimar Republic style exceptions to those rights, you lose a society that is protected against authoritarianism. Instead, you get a society that's just an incubator for totalitarianism.

My activism would be related to moving closer to a society where the starting floor hasn't fallen out for others based on class, race, and gender. Nazism, you know, kinda gets in the way of that.

Study the Weimar Republic. Explicit activism of the type you mention above (following an ethos of "By Any Means Necessary") was precisely the kind that set the stage for Nazis to come to power. Also, you should note that the "floor" in the US, even for "groups disadvantaged by class, race, and gender" is quite high in absolute terms. As Dinesh D'Souza's friend once observed, "I want to come to a country where the poor people are fat and own VCRs." There are people whose "floors have fallen out," but I don't think the existence of Neo-Nazis has had much affect on them. Can you give me an example where people demonstrating have made poor neighborhoods poorer? I can give you examples where riots have done that, but those were not sparked by Neo-Nazis.

Groupthink may be groupthink, but you know how we combat that – we fund public education.

The way to combat groupthink in the long term is to advance groups. One interesting thing that Thomas Sowell brings up in his book Race and Culture, is that Russians, Poles, and Italians started out having IQ score disparities as large as those of US black communities, but caught up over the time span of the 1st half of the 20th century. By 1950, the scores had basically equalized. He also notes a study of black children of GIs growing up in Germany, who showed comparable IQs to other children growing up there. Yes, there is clearly systemic racism in the US. It can be seen in the rising crime rates and decay of communities. (As a black man who was born in North Carolina and went to school in Harlem, Thomas Sowell has an interesting personal take on this.) I think it takes the form of incentives that encourage broken homes and abet poverty. (This can be seen in an increase in the IQs of black children in the early 20th century, which ended and reversed after the introduction of perverse incentives in the 1960's and 70's.) I think it takes the form of politics which protects public schools and keeps market buying power out of the hands of parents who want to help their children to advance. If one studies immigrant groups, one finds a pattern of groups that advance themselves in spite of overt oppression codified into law and sometimes enacted as violence. One also finds a pattern of groups, whose leaders keep their people in cultural isolation in order to maintain their power. Such patterns are found all over the world, and repeat themselves across cultures and in different times. I think it should now be obvious such patterns are at play in the US.