There are many widely recognized exceptions to free speech.
(Counterfeit money, for example.)
Supporters of Popper’s position, like me, want “incitement to intolerance and persecution” to become and remain one of those exceptions.
Censorship (beyond enforcing this limited set of exceptions) is usually a tool of intolerance and persecution. The whole goal is to build an open and just society so widespread, arbitrary censorship is not OK.
As I wrote in my “Blank is great”, it’s possible to call a lot of things “speech” and say it’s axiomatically good because of that. I can call censorship and bookburning “speech” to protect it. I can call the death fatwa on a controversial author “speech” to protect that fatwa. But, that’s the kind of “speech” I’m opposing here. I’m opposing “speech” that destroys other speech.
Yusuf Islam (“Moon Shadow” guy) got widely, career-endingly deplatformed for expressing (in speech) support for, and agreement with, the (also speech) calls to kill Salman Rushdie.
And that’s common sense to everyone. You don’t go around killing people. You don’t say “but my killing them is ‘speech’ and therefore protected”.
Same goes for harassment. It’s fine to ban it and block it.