It is not only the prisoners who grow coarse and hardened from corporal punishment, but those as well who perpetrate the act or are present to witness it.
There are limits to the smiles and scowls of diplomacy. Armies and missiles are not stopped by stiff notes of condemnation. They are held in check by strength and purpose and the promise of swift punishment.
It took the Church until 1832 to remove Galileo 's work from its list of books which Catholics were forbidden to read at the risk of dire punishment of their immortal souls.
The contagion of crime is like that of the plague. Criminals collected together corrupt each other. They are worse than ever when, at the termination of their punishment, they return to society.
Speaking generally, punishment hardens and numbs, it produces concentration, it sharpens the consciousness of alienation, it strengthens the power of resistance.
Capital punishment kills immediately, whereas lifetime imprisonment does so slowly. Which executioner is more humane? The one who kills you in a few minutes, or the one who wrests your life from you in the course of many years?
But secondly you say 'society must exact vengeance, and society must punish'. Wrong on both counts. Vengeance comes from the individual and punishment from God.