So that's the stance "the liberties of the intolerant should be limited only insofar as they demonstrably limit the liberties of others" most of the major social networks take and it falls short in that it's hard to draw that line. (also the ideas of constitutional safe guards applying to private entities is a whole other can of worms; id argue the speech the government can limit should be a subset of what any given private moderator might choose to)

Two examples: what im going to call the "im not touching you" type of harassment -- that is posting things clearly designed to hurt and wouldn't make sense in context unless designed for harassment. The platonic example here is the image macro that's the trans flag with the words "Your parents will burry you with the name they gave you". Cuel to the extreme, but doesn't technically call for violence against the given person, or the protected group at large so twitter and facebook, etc happily leave it up (and people wanting to be assholes hyper optimized pretty quick; ive seen the macro posted by multiple people in multiple places).

Second being the idea of stochastic terrorism. Painting a group as an unchecked evil means you don't have to tell anyone specifically they should commit violence, but, it's hard to be surprised if they come to that conclusion. See the shootings in Charleston or Christchurch.