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When people start revenge flagging they don't usually care much about their reputation... look just how much trouble @r4fken has caused when he started revenge flagging just about everyone and how much time it took for the issue to be resolved. Imagine tens of people like that that not only flag you inappropriately, but bring you negative balance... this will just drive away more people that it will help the platform.

There will always be bad actors on any scene, I agree that such a feature could be abused but in the same time (or more than being abused) could scare all the plagiators and eliminate majority unwanted authors. Don't you think?

No, not really... if they have nothing to lose how will it scare them.
Most of them don't get to stay for long as they usually are caught at some point if they continue with non original content claiming it is their own.
What is much more important is not to encourage such people that are in for some quick bucks and they will just stop coming.

It looks ok but what if a certain member will go mad and flagged authors like what happen few days ago. This kind of author doesnt seem to care if his reputation will lost which makes it unfair to those who cares.

Those are exceptions I think - "certain member will go mad". Members are generally responsible for their actions here.

The possible reason why an author could go mad is due to jealousy, jealousy of not getting vote while others are earning a lot.