Assuming rationality and egoism, it has always been difficult to explain why people punish violators of norms and agreements. Punishment has been considered a classic free rider problem. Everyone receives the benefits of punishing violators or defectors. Norms are maintained, and the example deters future malfeasance by others. But the cost is born entirely by the punisher, and these can be high. Those who carry out punishments effectively are engaging in an act of altruism. . . well, sort of. New research suggests that punishment may be its own reward.
“As the journal Science puts it, the study reveals what goes on in Dirty Harry’s head when ‘he succinctly informs a norm violator that he anticipates deriving satisfaction from inflicting altruistic punishment’. . .
The researchers determined that deciding to impose this penalty, an altruistic punishment, activated a brain region, the dorsal striatum, involved in experiencing enjoyment or satisfaction.” (Read on, here. And those with access to Science can read the full report of the study “Sweet Revenge?” in volume 305, pages 1246-1247)