> they use that platform to gather followers under the direct purpose of separating the white race from the blacks or the Jews or whoever the hate-object-of-the-week is
I find the sort of speech you describe highly unsavory, but I also disapprove of many other messages. Many people would advise Twitter to suppress the speech of gay people or immigrants, all the groups they hate.
The point of speech being speech is that it doesn't harm anyone. If some unsavory group manages to get 5K followers then I'd like to be aware of it and see what they are talking about.
Also, for the purpose of law enforcement, public Twitter activity could constitute signals intelligence to help stop crimes.
The idea that words have consequences (as you describe) is one of the most anti-liberty ideas in our modern culture right now. It's behind everything from unconstitutional "material support of terrorism" charges based on speech, to prosecuting journalists who report on classified information under the espionage act, to trigger warnings on works of classic literature, etc.
By censoring politically charged accounts Twitter likely benefits those groups by allowing them to skate by with coded speech in public but then keep their private rallying cries away from public scrutiny.
Keep in mind also that as a company, Twitter will be under pressure from interest groups and governments worldwide to suppress speech. Should we be allowed to criticize China on Twitter? Well, not if the China market becomes important enough to Twitter's revenue.
By failing to adopt a firm stance against censorship, Twitter has greatly damaged its credibility as a platform and opened the door to all sorts of censorship requests.
There are enough moralistic gatekeepers in the world, why should Twitter be another?