Gil is right on target when he separates government activity that seeks to prevent harm to the state and activity that seeks to confer a benefit on the state. In fact, our legal system also makes a distinction between the two. When determining if the government has performed a taking of property requiring compensation according to the Fifth Amendment, the courts have noted that when the government acts to prevent harm, no compensation is required, but when the government acts merely to create a benefit, compensation to the owner is required. If the same standard were applied to David's argument above, the benefit-conferring act of preserving prisoners' lives would be set apart from the harm-preventing act of the war on terror. This is why the rationale proposed for opposing the death penalty in the original post and in David's response are wrong. Were it true that there is a sufficient benefit to prolonging people's lives, it would mean that killing anyone ever would be a bad thing. And I doubt very much that the author believes that (killing in self-defense and in war come to mind).

If capital punishment is a bad thing, it's bad not because there is some benefit to society still to be gained in the prisoners (after all, it would be benefitial to society to ban smoking and alcohol altogether and few libertarians are arguing for MORE government restriction) but because of something else. David's rationale are utilitarian in their entirety. They are based only on how much good can be gained or how much harm can be prevented by preserving prisoners' lives. The utilitarian conception is completely lacking in room for human rights. The very definition of a right is something that is possessed and retained by a person even though such possession may not be good for society as a whole. I personally, and a great many other people, do believe in things like legal and human rights. One of them is the right to life. And unlike the rights to freedom and autonomy which can be curtailed in individuals who too greatly infringe other peoples rights (like criminals),
the right to life is not one that is capable of being limited without killing the person. Thus, the object of the death penalty is not to prevent further infringement of a person of other people's rights, but to punish, to take revenge on a criminal. And I am not willing to support punishment or revenge as an object.

If the death penalty were the only solution for preventing the infringement of others' rights, then it would serve a purpose other than revenge. But, since life imprisonment does fulfill that objective, capital punishment infringes too much upon the rights of the criminal.