Malcolm Harris is a fascist. A fascist attacking other fascists. Both are despicable.

The ostensible reason for this free speech for extremism is to keep the marketplace of ideas open

Should we not have kept this "marketplace for ideas" open for civil rights? Gay rights? Abolitionism?

But liberals are making a category error: White supremacy isn’t a source of information

He fundamentally doesn't understand the problem with censorship. Free speech exists to protect the obscene. Free speech isn't necessary for things considered acceptable. Nobody is going to stop you from saying "murder is bad" or "I like cheese." Yes, people want to stop you from saying "white power." Yesterday, people wanted to stop you from saying "black power." We cannot know what will be considered acceptable tomorrow.

When you censor, you're saying "I don't trust other people to make rational decisions." You know what's right and what's wrong, and wrong speech must be censored to protect the stupid. You know what? I'm neither stupid nor gullible. Furthermore, I disagree with your definition of "wrong." You have no right to impose your morality on me. I believe censorship is as wrong as fascism (in fact, censorship is fascism). Am I allowed to censor your speech encouraging censorship? Or are you the only one who gets to decide what's censored? Or is it the masses? If 51% of people agree something is wrong, we can censor it? So the majority can oppress the minority?

All censorships exist to prevent anyone from challenging current conceptions and existing institutions. All progress is initiated by challenging current conceptions, and executed by supplanting existing institutions. Consequently the first condition of progress is the removal of censorship. —George Bernard Shaw