Have you actually browsed them? When this thing hit the front page of HN I checked it out and while they say a lot of nasty stuff about people there I couldn't find an occurrence of organising online or offline harassment.
That is the organizing of harassment. That's what it looks like. People are very rarely dumb enough to post "I think we should commit a crime, who's with me" on the Internet.
Post enough slurs about queer people and somehow the harrasment happens without anyone having been explicitly told to do it.
Post enough slurs about Muslims and someone will eventually shoot up a mosque in New Zealand.
They'd do that anyway.
Personally, as a gay woman, I prefer letting people say slurs because then I know who to avoid. (Which isn't to say that I think services/people can't set their own rules - Cloudflare and DDoS-Guard are within their rights to drop KF as a customer). Stopping people from calling me a dyke or carpet-muncher doesn't make them not homophobic, it makes it harder for me to suss out who to avoid.
Freedom of Expression, and to a larger extent, social media, allows icky people to identify themselves for you.
Who wants to turn that off...and why?
The original claim was that it posed a direct actionable threat to someone's personal safety. This claim was not substantiated. Now you're shifting it to, "unflattering words are a form of violence."
The world would be a nicer place if these people preferred the former activity but that's neither here nor there.
Problem with this line of thinking is it generalises very well. E.g. talk enough about the evil things the USA does in the Middle East and eventually someone will fly a plane into some towers. Should we stop letting people say bad things about the USA?