There is a marvelous article by Dr. Edward Feser at The Public Discourse supporting capital punishment.
An excerpt with links at the jump.
“Most critics of capital punishment pay little attention to the question of “punishment,” focusing almost exclusively on their argument with “capital.” This is a fatal mistake, for as it happens, anyone who agrees that punishment as such is legitimate cannot fail also to agree, if he thinks carefully about the matter, that capital punishment can be legitimate, at least in principle. Of course, some critics of capital punishment reject punishment of any sort, but Christopher Tollefsen (who, in a recent Public Discourse article, claimed that capital punishment is intrinsically immoral) presumably would not.
“Traditionally, the aims of punishment are threefold: retribution, or inflicting on a wrongdoer a harm he has come to deserve because of his offense; correction, or chastising the wrongdoer for the sake of getting him to change his ways; and deterrence, discouraging others from committing the same offense. Retribution is necessarily the most fundamental. Strictly speaking, we cannot correct someone who doesn’t deserve correction; at most we might try to affect his behavior (via drugs, say) in a sub-personal manner that doesn’t appeal, as true correction does, to his sense of desert and shame. We also cannot justly inflict a punishment on someone for purposes of deterrence unless he deserves that punishment. That retribution is fundamental doesn’t entail that those with the authority to do so must always exact retribution on an offender. It does, however, mean that retribution may be exacted, all things being equal (though of course things are not always equal); it also means that retribution—inflicting a harm that is deserved—must always be part of any act of punishment, even if it is not the only part.
“Now, what a wrongdoer deserves as punishment is a harm proportionate to his offense. If we allow that someone guilty of stealing $100 deserves to be punished, we must also acknowledge that he ought not to be punished by having $100,000 taken from him, or by having merely ten cents taken from him; he has not done anything to deserve the harsher punishment, but he does deserve more than the lesser punishment. In short, the punishment should fit the crime. This does not mean that a wrongdoer should have the same wrong inflicted upon him that he has committed against others—that rapists should be raped, or that arsonists should have their houses burned down. Sometimes inflicting such punishments would be impossible (a mass murderer cannot be executed multiple times), or would do more harm than good. The point is rather that the gravity of the punishment should reflect the gravity of the wrongdoing. Hence those guilty of large thefts should be punished more severely than those guilty of small ones, those guilty of inflicting serious bodily injury should be punished more severely than those merely guilty of theft, and so forth. This principle of proportionality might, in some cases, be difficult to apply practically, but we cannot plausibly reject it without rejecting the notions of desert and punishment along with it.
“If wrongdoers do deserve punishment, and if punishment ought to be scaled to the gravity of the crime (harsher punishments for graver crimes), then it would be absurd to deny that there is a level of criminality for which capital punishment is appropriate, at least in principle. Even if it were claimed that a single murder would not merit it, it is not difficult to imagine crimes that would. Ten murders? Ten murders coupled with the rape and torture of the victims? Genocide? If wrongdoers deserve punishment and the punishment ought to be proportional to the offense, then at some point we are going to reach a level of criminality for which capital punishment is appropriate at least in principle. To claim that no crime could justify capital punishment—to claim, for instance, that a cold-blooded genocidal rapist can never even in principle merit a greater punishment than the lifelong imprisonment inflicted on a bank robber—is implicitly to give up the principle of proportionality and, with it, any coherent conception of just punishment.
“Obviously, questions might be raised about whether capital punishment is advisable in practice, even if it is allowable in principle. Enough has been said, however, to show that it is not intrinsically wrong to resort to it, at least not if punishment as such is legitimate. (For a more detailed defense of capital punishment along similar lines, see chapter 4 of David Oderberg’s Applied Ethics.)
“Now, why does Tollefsen think that capital punishment is intrinsically wrong? He appeals to what he calls the “Essential Dignity View” of human beings, according to which “human beings … possess dignity, or excellence, in virtue of the kind of being they are; and this essential dignity can be used summarily to express why it is impermissible, for example, intentionally to kill human beings: to do so is to act against their dignity.” On this basis, Tollefsen concludes that “it is always wrong intentionally to kill a human person,” from which it follows that capital punishment is wrong.
“It is one thing merely to assert that capital punishment is against human dignity; it is quite another actually to show that it is. To be sure, it is plausible to say that to kill an innocent person is to act against his dignity. It is also plausible to say that imprisoning or fining an innocent person is contrary to his dignity. Suppose, however, that someone claimed that imprisoning or fining even a guilty person would be contrary to his dignity. I assume Tollefsen would disagree; certainly he should. The reason is obvious: A guilty person deserves such punishment, but an innocent person does not. So if a guilty person can, consistent with his dignity, deserve imprisonment or a fine, why could he not also deserve capital punishment, if his offense is grave enough?”