“An eye for an eye” is one of the strongest human instincts—and one that can be difficult for both individuals and societies to overcome—but decades of psychological evidence show that reciprocating harm is not always the best course of action. Punishment, when meted out fairly, can work to condition people not to repeat misdeeds, and threats of negative repercussions can act as powerful disincentives.
On the other hand, punishment can easily be subsumed by a desire for revenge, or greatly exceed the offense committed. Over-zealous punishment is rarely an effective deterrent and may cause negative effects that extend beyond the one being punished. A hyper-reactive “tough on crime” position that favors punishment over rehabilitation, for instance, has arguably contributed to an overpopulated prison system with high rates of recidivism.
Punishment has its place—but the ability to rise above baser instincts and judge each situation objectively, and with an eye toward fairness, is one of the highest achievements of humanity and of civilization.