I think you tried to solve the problem the wrong way. A better solution (in place of the invitation system), would be to create a more advanced access control system which would group the problematic users. Grouped users would be able to see normal posts and posts of their peers, but their own posts wouldn't be displayed to normal (non-problematic) users.
Think of it like shadowbanning with a echo-chambering vibe.
Trolls would be in one group, funny comments in another. Alt/far right/left groups could be children of some of the previously stated ones.