This kind of setup imposes a cost for rude, nasty, aggressive and destructive behavior - since you can simply be excluded from the group in that case.

This is how most of the world works on a day to day basis; you don't let random people into a corporate strategy meeting or an academic council meeting. You only admit people who agree to abide by civil society rules.

Something like that can be incredibly useful, but it requires a lot of up-front organizing effort. Also, malicious types have been known to sneak into say, a closed mailing list, and leak the internal discussions to Twitter or whatever, so...