European governments are adamantly opposed to capital punishment -- the EU bans it outright -- and some Europeans consider its use in the US barbaric. Indeed, many European intellectuals argue that not just capital punishment, but punishment in general, does not deter criminals.
Whereas Europeans, with crime rates well below US rates for the past half century, could once afford to be relatively "soft" on most crimes, they have seen their crime rates increase sharply during the past 20 years. By contrast, US rates have fallen, in part because of greater use of punishment.
This includes capital punishment. I support executing some people convicted of murder because -- and only because -- I believe that it deters other murders. If I did not believe that, I would oppose capital punishment, because revenge and other possible motives should not be a basis for public policy.
Serious empirical research on capital punishment in the US began with a pioneering study by Isaac Ehrlich, published in 1975 in the American Economic Review. Some subsequent studies have sometimes found a much weaker deterrent effect, while others have found a much stronger effect. The available data are quite limited, however, so one should not base any conclusions solely on the econometric evidence.
Of course, public policy on any punishment cannot wait until the evidence is perfect. But, even with the limited quantitative evidence available, there are good reasons to believe that capital punishment deters.
Most people, and murderers in particular, fear death, especially when it follows swiftly and with considerable certainty following the commission of a murder.
As David Hume put it in discussing suicide: "No man ever threw away life, while it was worth living. For such is our natural horror of death."
Likewise, Schopenhauer believed that "as soon as the terrors of life reach a point at which they outweigh the terrors of death, a man will put an end to his life. But the terrors of death offer considerable resistance."
Opponents of capital punishment frequently proclaim that the state has no moral right to take anyone's life, including that of the most reprehensible murderer. Yet that is absolutely the wrong conclusion for anyone who believes that capital punishment deters.
To see why, suppose that for each murderer executed -- instead of, say, receiving life imprisonment -- the number of murders is reduced by three, which is a much lower number than Ehrlich's and some other estimates of the deterrent effect. This implies that for each murderer not executed, three innocent victims would die. In fact, the government would indirectly be "taking" many lives if it did not use capital punishment.
Saving three innocent lives for every person executed seems like a very attractive trade-off, and even two lives saved per execution seems like a persuasive benefit-cost ratio for capital punishment. Admittedly, however, the argument in favor of capital punishment becomes less clear-cut as the number of lives saved per execution falls. But even if only one life were saved per execution, the trade-off might still be desirable if the life saved is much better than the life taken, which would usually be the case.
Many people object to comparing the quality of the life spared and the life taken. Yet I do not see how to avoid such a comparison. Consider a career criminal who robs and kills a victim who led a decent life and left several children and a spouse behind. Suppose it would be possible to save the life of an innocent victim by executing such a criminal. To me it is obvious that saving such a victim's life must count for more than taking the criminal's life. Obviously, not all cases are so unambiguous, but a comparison of the qualities of individual lives must be part of any reasonable social policy.