I don't oppose the death penalty because it is wrong it kill people who commit heinous crimes. I oppose the death penalty because it is unncessary. Human life should only be taken when necessary, such as in self-defense, war, preventing terrorist acts. Retribution will neither bring the victims back to life or aid in the healing process, nor is it a valid basis for public policy.
Even though I oppose the death penalty, I do so on practical grounds, and do not find common cause with those who oppose the death penalty on radical grounds. Mumia Abu-Jamal is probably one of the most deserving of death. And if in the heat of his crime, his death could have prevented the loss of an innocent life, so be it. But what purpose would his death serve, 20 years after the fact?