I know Steemit have withdrawn delegation in the past, but I do not know their process for doing this. There are lists on Github. Each Steem front end can decide to filter out posts from certain users.

No platform can be perfect. Steem will be whatever the users make it and some will choose to abuse their freedom. Would you sacrifice your freedoms to stop them?

I work with @steemflagrewards to try and make it less profitable to exploit Steem, but we have limited SP between us. That can earn me some big flags, as in several dollars worth, but I think it needs doing.