While I have backed-off on my full support for capital punishment, I don't shed tears if a murderer is executed. Some would claim that I am being hypocritical to oppose abortion yet support capital punishment. My qualification to wanting to protect life is that I'm most concerned with INNOCENT life. So, an unborn child that has never hurt anyone -- whose only "crime" was to be conceived -- should be protected and allowed to be born. But, the person who chooses to kill another person when its not a self-defense or war situation is a person that I don't feel much compassion for. They can pass on to their reward for all I care.
If someone pointed out that God forbids us from killing, then I would agree with that and would accept the alternative of a TRUE life sentence. The problem with life sentences has been that they are often not really life sentences. Time is given off for "good behavior" or whatever and these killers find themselves walking our streets again. If people got true life sentences for first or second degree murder, rape, child molestation and a few other series offenses, I would say, "OK, you can dispense with capital punishment." Besides, there have been instances where innocent people have been convicted and put to death, and that is my other reservation regarding the death penalty -- you can't take it back.
Another idea: Since we are allowing these killers to live, and we will support them for decades in our prisons, let's get some use out of them. As part of the life sentence and avoiding the death penalty, they must agree to participate in medical research for the benefit of mankind. If they already have some disease (e.g., AIDS, cancer, etc.), then we could test experimental drugs and treatments that we wouldn't be able to otherwise use human subjects for. In this way, these criminals could start to re-pay society for the horrible crimes they committed. I don't advocate making the experiments deliberately painful or unnecessarily dangerous -- I'm not talking torture or revenge here. I'm just saying, we spared their lives (something their victim(s) didn't get), we're paying to house and feed them for a long time, so why not recoup some of that generousity by getting benefit back from this incarcerated population of murderers?