The death penalty is not simply "punishment." The primary purpose is to rid society of a danger. If a family dog attacks a child, no matter the reason, we kill the dog. Putting a mass-murderer in prison for life is not justice, because then the same society which was victimized by the guilty in the first place is twice victimized by having to literally pay for the crimes by caring for and maintaining the guilty for life. And to say the death penalty is not a deterrent, it is an absolute deterent for the guilty who are put to death.