[dan1123]

People kill when they shouldn't — fact. Obviously, when they do, they haven't been "deterred". If they had been "deterred", we would never know about it. For this reason, I consider talk about "deterrence" to be a smokescreen.

I have three objections to that. First, people do everything when they shouldn't. This doesn't mean that there should be no consequences. Second, you do know in aggregate if deterring methods worked, because you can see the incidence rate drop. Third, the cost of committing an act is based partially on the potential consequences of the action and how likely those consequences are to occur. If a "deterrent" is removed, then the cost of the act is reduced.

[thulldud]

I am objecting to the insistence that capital punishment must satisfy some standard of "deterrence" before it is justified. Anti-capital punishment advocates tend to feature this sort of reasoning, trumping justice with pragmatism.

They aren't concerned with aggregate measures anyway, since their real goal is to do away with all punishment. Accordingly, they focus on individual murderers that weren't "deterred" as proof that deterrence doesn't work; then they throw out the baby with the bathwater.

Just for the record, I will say that I have no doubt that capital punishment is deterrent; I am just pointing out that deterrence is not the reason for it.