https://mobile.twitter.com/pewdiepie
Hate speech doesn’t need legal protection as a term to be against the rules of the site. I can’t remember if that’s the actual term twitter uses, but it’s the spirit of their rules.
We could have a wider debate about whether our public square should be privately owned (I don’t think it should) but that wasn’t your point.
Edit: more details and reason why his tweets are (self)deleted
