You may agree with private entities censoring now, because you disagree with the censored statements. What if the roles are reversed? What if Mark Zuckerberg runs for president and uses his platform to this end? What if whomever-you-disagree-with pays private entities to censor your newspaper / internet site?
Democratically defined censorship, enforced by the state is one thing (and already complicated). Censorship without all those guarantees is, IMHO, quite another.