The censorship we are talking about is not censorship: it's moderation. Every forum worth using has moderation. The problem today is that most people aren't using user-moderated forums. Instead, they are using corporate-moderated social networks.
Murder, theft, cigar smoking in enclosed spaces... you name it, the only way to counteract malignant behaviors is to punish transgressors in order to obstruct the activity to the extent that a) we prevent it from growing, and b) we can tolerate the persistence of the activity at some diminished level of intensity.
Free speech requires us to strike a balance, like fighting crime. Driving hate speech underground successfully hides it from public view so that folks who don't want to swim in that cesspool can avoid it, the same way we hide porn from eyes who want to escape it. And the fact is, ever smarter tech methods can do this increasingly well, despite what Facebook claims.