duewell,
Thanks for such an excellent reply! Permit me to edit it (mostly grammar)...
We should not kill nor should we murder. Does it matter what justification one uses for ending another's life? Is that something a killer should take before God in their judgment? Any killer could rationalize or justify why they took someone's life. One could do the same to justify almost any sins they commit. We do not justify our sins, we repent of them! Jesus said, "By the same measure in which we judge, so too shall we be judged".
When I hear this kind of question, I think of Moses. When God decided that he would take the first-born sons of Egypt, he sent an angel to do His work. None of us, except the returned Christ, are here to dispense God's justice - God and His Christ are quite capable of doing that.
Will any of us stand before God (except the Christ) and justify ourselves and our actions? Our duty is to pray for the unrepentant sinner, in the hopes that God will open their heart and lead them to repentance. If anything, we should do all we can to prolong the life of an unrepentant sinner. We know the judgment they will face and do not wish for any to be damned - we pray for them to 'see the light'. As Christians, we follow and enforce God's laws on ourselves in the hopes that our example will lead others to do the same. It is not our job to enforce God's law on others, God and His Christ are far more capable than us to do so. Have faith in God's/Christ's justice. And understand, in the end, all things serve GOD/GOOD.
-Duewell (edited by Brad Watson, Miami)