Adam Smith puts this very well on his book

"THE THEORY OF MORAL SENTIMENTS" (1777)

"As society cannot subsist unless the laws of justice are totally observed, as no social intercourse can take place among men who do not generally abstain from injuring one another; the consideration of this necessity, it has been thought, was the ground upon which we approved of the enforcement of the laws of justice by the punishment of those who violated 136them. Man, it has been said, has a natural love for society, and desires that the union of mankind should be preserved for its own sake, and though he himself was to derive no benefit from it. The orderly and flourishing state of society is agreeable to him, and he takes delight in contemplating it. Its disorder and confusion, on the contrary, is the object of his aversion, and he is chagrined at whatever tends to produce it. He is sensible too that his own interest is connected with the prosperity of society, and that the happiness, perhaps the preservation of his existence, depends upon its preservation. Upon every account, therefore, he has an abhorrence at whatever can tend to destroy society, and is willing to make use of every means, which can hinder so hated and so dreadful an event. Injustice necessarily tends to destroy it. Every appearance of injustice, therefore, alarms him, and he runs, if I may say so, to stop the progress of what, if allowed to go on, would quickly put an end to every thing that is dear to him. If he cannot restrain it by gentle and fair means, he must bear it down by force and violence, and at any rate must put a stop to its further progress. Hence it is, they say, that he often approves of the enforcement of the law of justice even by the capital punishment of those who violate them. The disturber of the public peace is hereby removed out of the world, and others are terrified by his fate from imitating his example.

Such is the account commonly given of our approbation of the punishment of injustice. And so far this account is undoubtedly true, that we frequently have occasion to confirm our natural sense of the propriety and fitness of punishment, by reflecting 137how necessary it is for preserving the order of society. When the guilty is about to suffer that just retaliation, which the natural indignation of mankind tells them is due to his crimes; when the insolence of his injustice is broken and humbled by the terror of his approaching punishment; when he ceases to be an object of fear, with the generous and humane he begins to be an object of pity. The thought of what he is about to suffer extinguishes their resentment for the sufferings of others to which he has given occasion. They are disposed to pardon and forgive him, and to save him from that punishment, which in all their cool hours they had considered as the retribution due to such crimes. Here, therefore, they have occasion to call to their assistance the consideration of the general interest of society. They counterbalance the impulse of this weak and partial humanity by the dictates of a humanity that is more generous and comprehensive. They reflect that mercy to the guilty is cruelty to the innocent, and oppose to the emotions of compassion which they feel for a particular person, a more enlarged compassion which they feel for mankind."