Online or not, and social group must be protected from bad actors or they will drive everyone else away. As an example, long ago I knew of a group for single adults which had one creepy guy who drove away all the women, and of course their absence drove away the men. The creator of the group took the lesson, and started a new group which required permission to join; the way it worked was you would briefly talk with the founder, and as long as you didn’t seem like a creep you were in.