I’ve been exploring (as opposed to participating in) message boards since I was learning how to multiply. The first rule seems to be “Stay on topic!” That means no politics on a knitting board.
If the board is privately owned and operated, the owner gets to decide everything, including whether and when to self-destruct by not enforcing rule #1.
I no longer believe that is tolerable in cases in which the owner controls a significant quantity of mass communications. Little po-dunk sites that have insignificant levels of traffic, sure, but when you have millions of users, you become part of the public commons, and cannot be allowed to control speech at that level.
I regard it as a threat to our system of governance to allow any entity to censor so much public speech. China already forces Google, Facebook, Youtube, and so forth to censor speech they don't like.
Letting corporations get away with this behavior will simply result in governments pressuring them to censor speech as these governments direct.
It will become back door censorship of freedom of speech by any totalitarian government on the planet.