That's a pragmatic theory, but in a reality there's also a little of irrational need for eye-for-an-eye revenge in an act of the punishment of a wrongdoer, peop

That's a pragmatic theory, but in a reality there's also a little of irrational need for eye-for-an-eye revenge in an act of the punishment of a wrongdoer, people need that to feel that the justice was really met. It's an atavistic urge, lynch mob instinct to hate those who you see as a danger to your group. And yes it's not very rational or ethical, certainly not very civilized, and we can pretend we don't feel that way, but it's a part of a human nature. People who follow the rules expect to see those who break them punished as a proof that the system works; it makes them feel safe and content (and also reinforces social norms, as you've said).