There is some control over who stays.
Most may not be aware, but this forum does in fact have an active moderator. I do quite a bit of flagging of spam posts and have exchanged emails with this individual on a few occasions. This person can and does ban / delete users - and remove spam and offensive posts (for example, pretty sure an ID posting on the Skilled Worker section of this forum was turfed yesterday for impersonating a vip member). So we aren't entirely unsupervised.
Having said that, we are largely unsupervised.