There is a simple way to deal with shitty users. The problem is that it runs counter to the interests of the organization that hosts them. Require every user on the platform to use an invitation code from another user. They don't have to use their real names, but if they do something fraudulent or awful both the inviter and the invitee get banned.

This is why Dribbble is still nice and most other places turn to garbage.

HN is a rare exception. It's likely because the subject matter requires a certain degree of intelligence, which tends to negatively correlate with trashiness.