Now, here is an interesting flip-flop. More Republicans favor a death penalty than Democrats. Republicans are pro-life, Democrats are pro-abortion--even up to full term. Liberal democrats frequently quote the Bible and say, "Thou shalt not kill". (Yes, that is ironic.) To help you understand why pro-lifers are sometimes also pro-death penalty, it may help to know that the Bible does not say, "Thou shalt not kill". The actual translation is, Thou shalt not MURDER.
If you think about all the wars the Jews fought in Old Testament times under God's direction, the commandment to not kill would not make sense. David, the hero in David vs Goliath, would be breaking a commandment if the rule was not to kill.
The Jews were told by God to use stoning as their method of capitol punishment. Murder on the other hand is premeditated, something done out of anger. I think most people are conflicted about this one, even if they know it says thou shalt not murder.
The other problem with the Death Penalty is that there is such a time lag between the verdict and the execution. That delay diminishes its effectiveness as a deterrent. It is not a make or break issue for me.