The old common law outlawing, shunning, or ostracism.
Game theory says that if the good people shun the psychopaths. the cheaters, they have no effect.
Unfortunately you have to give the psychopaths a few hits early on so they demonstrate their evil.
But once you kick them out, ignore them, withdraw your support, they are powerless.
The old English common law outlawry was expulsion from the community or society and every mans hand would be against the outlaw with no blood debt or repercussion for any action against them.
The trick today is to be creative in making a de-facto outlawing take place.
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