The is no single default but there are entire hosts of different defaults that will work across different communities and some norms that ought to exist across all communities. Hacker News wont let me abuse you verbally and if I make a credible threats of violence against you most places OUGHT to lock me up in order to prevent you from being murdered. Turns out there are TONS of reasonable defaults, some of which we can arrive at by simple logic others which we can arrive at by trial and error.
It would be shocking if communication was literally the only area of human endeavor which couldn't or shouldn't be regulated. Stranger yet to pose the idea on a moderated forum. Turns out authoritarian solutions do work.