What a platform chooses to ban or allow decides the shape and direction that platform takes. It's the reason why you're on Hacker News and not 4chan right now, HN is a strongly moderated platform with expectations for how users should treat each other. We saw how quickly Twitter degraded when it became a free for all.
That said, I think having "open spaces" on the internet is important. 4chan used to be that kind of free-for-all space where anything goes and you had to leave your moral outrage at the door. Thing is that it was self-contained. Now it feels like the entire internet is being turned into 4chan. Facebook ideally for most people, is a place where you go to see your friends' baby and pet photos, not get called slurs by strangers.
