nota bene said:
What's that argument? Very curious because I'm among the "staunchest of opponents."
Well, perhaps not an argument so much as a hypothetical example. It goes like this:
Let's suppose first that we have a principle: the death penalty is not to be applied in any case.
Next, let's suppose there is an absolutely murderous, very intelligent, and very physically capable, criminal who is incarcerated for some crime or other. This person's abilities are genuinely legendary (assume they're the result of some evil genetic experiment or something like that). While in prison, he or she begins murdering other prisoners, some of whom are incarcerated for such things as DUI or possession of marijuana. This person is put in isolation, but manages to escape, and then kills still more people.
This person has a cult following; if we find a cage strong enough to contain the supercriminal, stopping attempts to break out from the inside, then it becomes inevitable that their followers break them out from the outside.
So forth and so on: the idea is simply that we have someone on our hands who can defeat any attempt at incarceration, and the only way to keep them from killing others who in no way deserve to be murdered, is to kill the supercriminal.
It seems to me that in such a case, no reasonable person would support keeping the supercriminal alive. And if I'm right about that, then the principle we started with is incorrect. In at least one case, the death penalty should be applied.
But then we can start modifying the example: suppose rather than there being a 100% probability that the supercriminal will be able to escape and kill from any given cage, the probability is 99%. I think that, still, a reasonable person would think the death penalty should be applied. What about 98%? 97%? Etc.
People are going to have different instincts and intuitions about when we should start drawing the line, and I think this will reflect how they view the death penalty itself. Nevertheless, the point of the example is to point out that there are sometimes practical reasons we kill people.
Most of the time, I would agree, the death penalty is applied with at least a touch of vengeance in mind. This is why I say we use it too often, and usually for the wrong crimes. The death penalty is not really a deterent in most cases of murder, and it's hardly anything that someone who's seen the process up close would call justice. However, these are not the only elements of the death penalty that deserve consideration. My example is meant to bring out one that I think is neglected.