Let's go ahead and get this over with first, just to be sure that no one accuses me of being a fan of rapists or child rapists: rape is a horrible evil, and the rape of a child is even more horrible than the rape of an adult. Clearly rapists should be severely punished.
The question is, what should that punishment be? Should it be death? Rape seems such a horrible crime that death does not seem unreasonable. Yet there is an important reason to believe that capital punishment for rapists would be a bad idea, not for the sake of the rapists, but for the sake of their victims.
The problem is what economists call marginal deterrence. If the punishment for rape is execution, and if that is the same as the punishment for murder, then the marginal cost of committing murder after committing rape is zero. That is, punishing rapists with death gives them an incentive to kill witnesses, particularly their victim. The result of execution of rapists may be slightly fewer rapes, but possibly a significantly higher number of the remaining rapes may end up with dead victims. I am personally uncomfortable with the idea of reducing rapes at the cost of additional murders, particularly if these victims are children.
When deciding the punishments for crimes, the absolute punishment is not the only thing that matters. The relative punishment for different crimes also matters. Unfortunately there was no discussion (from what I have read, anyway) of this at all in the Supreme Court. My low opinion of the court remains unchanged.
I anticipate three possible responses to this argument (there are surely more):
- Marginal deterrence could still be preserved if rape + murder results in a higher probability of execution than rape alone, resulting in higher expected punishment.
- Punishment isn't about deterrence at all.
- Changes in punishment do not affect the behavior of criminals, i.e., deterrence doesn't work.