As we discussed previously, punishment is an imposition contrary to the will of a guilty party by the one responsible for the common good, in response to or by reason of that party's guilt. The ultimate goal of punishment is to uphold good and restrain evil.
Consequently, there are several difference reference points by which the severity of a punishment is to be measured, and deemed as appropriate, or as excessive and unjust. "A severe punishment is inflicted not only on account of the gravity of a fault, but also for other reasons" (I-II, Q. 105, A. 2, ad 9):
- Since punishment is a response to guilt, it should be proportionate to guilt. "First, on account of the greatness of the sin, because a greater sin, other things being equal, deserves a greater punishment." (I-II, Q. 105, A. 2, ad 9) "Just as punishment must be imposed on guilt so that the guilt may be ordered [the inequality of injustice equalled by punishment], so it is necessary that the severity of punishment correspond to the greatness of guilt " (St. Thomas Aquinas, In IV Sent., dist. 20, q. 1, a. 1, qa. 3)
- But at the same time, since punishment is imposed not for its own sake, but to prevent evils ("The punishments of this present life are more medicinal than retributive, for retribution is reserved for the divine judgment." ST II-II, q. 66, a. 6), the punishment should be proportioned to preventing evils. A greater punishment may be required to hold men back from evils to which they are more readily inclined, or which it is harder to discover and so punish, or which readily leads to still greater evils.. "Second, on account of a habitual sin, since men are not easily cured of habitual sin except by severe punishments. Third, on account of a great desire for or a great pleasure in the sin: for men are not easily deterred from such sins unless they be severely punished. Fourth, on account of the facility of committing a sin and of concealing it: for such like sins, when discovered, should be more severely punished in order to deter others from committing them." (I-II, Q. 105, A. 2, ad 9)
- But no more than is necessary for preventing evil: "The punishments of the present life are medicinal, and therefore when one punishment does not suffice to compel a man, another is added: just as physicians employ several body medicines when one has no effect. In like manner the Church, when excommunication does not sufficiently restrain certain men, employs the compulsion of the secular arm. If, however, one punishment suffices, another should not be employed." (ST II-II, q. 39, a. 4) "In the infliction of punishment it is not the punishment itself that is the end in view, but its medicinal properties in checking sin; wherefore punishment partakes of the nature of justice, insofar as it checks sin. But if it is evident that the infliction of punishment will result in more numerous and more grievous sins being committed, the infliction of punishment will no longer be a part of justice. It is in this sense that Augustine is speaking, when, to wit, the excommunication of a few threatens to bring about the danger of a schism, for in that case it would be contrary to the truth of justice to pronounce excommunication." (ST II-II, q. 43, a. 7)
What punishment suits a given crime depends, therefore, on two quite distinct considerations: (1) how great the crime is; (2) how necessary for or effective a given punishment is in preventing such crimes, in instilling a revulsion for such crimes in the mind of the public, etc.
There isn't an absolute punishment that is "deserved" for a given crime, which could be stated in advance, apart from a concrete community, a cultural, legal and historical context, in which a legal system establishes and imposes diverse and just punishments for diverse crimes, according to their gravity and the necessity and difficulty of keeping people from committing them, etc.
As far as merit and demerit in the civil sense are concerned, for a person to "deserve" a certain reward or punishment, is nothing other than for it to be just for the law or keepers of the law to appoint that reward to someone for his benefit to the community or that punishment for one who harms the common good.
We can, therefore, only say that a given crime deserves a certain penalty, such as capital punishment, if it would be just for a community to impose that penalty. If it would be excessive and therefore inappropriate for the community to impose that penalty, it doesn't make sense to say that the criminal deserves that penalty, unless we mean something along the lines of "committing such and such a crime could, in some context, be justly punished by such a penalty".
Consequently, while agreeing with the ultimate thesis of Edward Feser's and Joseph Bessette's work "By man shall his blood be shed: a Catholic defense of capital punishment", I maintain that capital punishment cannot be said to be "deserved" for certain crimes purely in the abstract, as is suggested in that work, but only where such punishment fosters the reduction of those crimes or the abhorrence of them among the public. On the (in my opinion, and I think fairly obviously) counterfactual hypothesis that some corporal punishment and shaming such as public whippings, as the severest punishment imposed by law, were in fact enough to deter convicted criminals and any future potential criminals from aggravated murder, genocide, or whatever other crimes, and instill an abhorrence for such crimes in the general populace, than such corporal punishment would be what the "just deserts" for those crimes in that civil and cultural context, and a severer punishment such as capital punishment excessive and unjust.