Death as a Deterrent?

Many in this recent aftermath of Osama Bin Laden being shot have brought up the death penalty as something that is obsolete. Many have taken the lead from John Paul II's aversion to capital punishment in modern society. One of the arguments I consistently see that seems to me the weakest and most refutable just by commonsense and common everyday observation is that death is not a deterrent.
I travel by subway quite often. The tracks down in the pit are common everyday rails except for the high one that stands a couple inches above the rest. There is a sign as well that says, "Danger Third Rail: Live". I don't see too many boys showing off for the girls by jumping down there and even pretending to touch it. No, death in such a case is a deterrrent. This is obvious. The prospect of being fried deters most---I have yet to see any. Sure there may be an isolated case of someone with such disordered passions that he will still touch the third rail (and this by no means disproves the presumption but actually in its rarity proves the case), but for the vast majority they don't touch it. Ask yourself, why?