It does not, however, mean that the punishment is not justified. As far as I am concerned, if you see fit to end the life of another person (unless it should happen as a means of self preservation, a defense of your own life) then you deserve to put under the death penalty. If you claim another life out of malic or greed or what have you, then as far as I am concerned you have through that act relinquished all right to your own right to continue living.
In my mind, not putting a murderer (one has as I said before, killed out of malic, greed, or any other reason other than self defense of their own life or a loved ones through some direct threat) then you devalue the life of the victim. It is, as far as I am concered, the same as saying that the life of a murderer is more valued than the life of the victim.
Some people will openly disagree with that standpoint and I can respect that, but it is my own personal opinion on the matter. I'll also add here that I agree with Ket, however, I am of an even firmer opinion. Some people cannot be reasoned with. Some people refuse to negotiate and some people or factions are only going to back down if they recognize that statements made to the point of 'This and this will not be tolerated' are going to be back up by threat of force.
Having said that, I do not believe we need to be war mongering, or looking under rocks for the next threat, but when and if the next threat presents itself, I personally feel safer knowing said threat might be a little bit more cautious to poke its head up if it knows that when it takes some action against this country or its citizens that it might get that head blown off if the situation warrents such a reaction.