I have a solution for situations like this.   

We create a web app that users can SteemConnect to.  If their account has a reputation over 55 and they have at least 1000 SP they get a vote on what to do in a situation like this. (That should limit gaming the system too much)   If the majority of those Steemians feel that the problem should be dealt with then the Witnesses and other high powered accounts will be asked to carry out systematic flagging to limit the abuse as much as possible instead of turning a blind eye.  

If the witnesses don't carry out the communities wishes then they risk having witness votes taken away.   

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