An unmoderated discussion forum quickly turns into a disaster. People have used Facebook (and WhatsApp) to organize violence and other "real-life" crime.

How is proposing an entirely credible alternative scientific theory "violence"?

Bars and restaurants are unmoderated discussion forums that have been used to organize violence and real-life crimes since forever. Who exactly do you think is wise and moral enough to police what everyone talks about?

Pretty sure most such places, as in very nearly all of them, have a line that if you cross it they will shut you down and/or ask you to leave or just throw you out. Not like most owners, bartenders or bouncers would be cool with someone trying to rally a mob in the place.

Sure. Even free speech extremists seem OK with cordoning off immediate plans to commit violence. But try to find a place where a waitress or bartender will interrupt your conversation to insist on the correct view on the flatness of the earth, whether the moon landing occurred, etc.

Facebook and Twitter consider themselves to be official arbiters of truth, and they are increasingly putting their hands over the mouths of people who espouse "wrong" views.