Ok Jim, I'm not going to go through comment by comment because I think that just gets really hard to read and gets us sidetracked from the real discussion, so I will identify a couple of the broader problems you had with my position and see what I can say about them
1. My biblical interpretation
First, the reason why I put in that initial proviso about "If I wanted to do a Biblical interpretation..." is because I'm not a believer and therefore don't require Biblical sources to make a judgment about morality. I don't know why I don't have a "right" to argue from a Biblical perspective, however. I was raised through Catholic schooling and have a fairly decent knowledge of the content.
You are correct to say that if I don't believe that Jesus is God I can't believe that everything he says is inerrant truth. But, considering that you do believe that, I think it is a useful thing for me to do. I may see Jesus only as a wise man ahead of his time, not God, but I don't think that renders all my interpretation invalid.
2. Jesus's Message
I was always taught that Jesus, in the new testament, created a new covenant - simply that we love one another as Jesus loves us, that we should love others as we love ourselves. Is this a correct interpretation? Is this the overriding message Jesus had for the people of earth? That is he message I get from the sermons on the mount and on the plain - love, forgiveness, turning the other cheek, not passing judgment on others, treating others as we would wish to be treated ourselves...
You disagreed repeatedly that Jesus told us to see him in all others... what is your interpretation of Matthew 25:31-40?
It is clear also that Jesus saw the value of those that society shunned, there are many examples of this.
Overall, I don't see what is wrong with my interpretation of how Jesus would have us treat other people, and I don't see any reason to believe that he would support the death penalty as a moral thing to do because of those teachings about how we ought to love and forgive.
3. God's relation to Caesar - the authority of terrestrial government
I don't really understand your position here.
You argue that the authority of the state on earth comes from God. I had a problem with this, as to me it implies that all that the state does it does through the authority of God. States, however, commit terrible crimes against people, crimes which I don't see anyone being able to defend - states murder and torture, they steal... do they do these things thanks to God's authority?
If the answer to that question is yes, then should we simply just passively accept that which states do? I don't believe you can argue that
If the answer is no, doesn't that then open up the possibility that the death penalty is potentially morally wrong?
I don't understand why you see there being a difference between the message Jesus had for his followers and God's giving of authority to the state. Is the state not simply the way humans organise themselves? Shouldn't those humans follow what Jesus taught them?
4. Efficacy
You disagreed that the effectiveness of the punishment should have a role in our questioning of the punishment's morality.
However, if you are going to argue that God gives the authority to the state to act in matters of a terrestrial nature, then one ought to judge the actions of the state through terrestrial means. In that case, the effectiveness of the punishment is inherently linked to its morality. If the punishment is a punishment which is not effective, that surely has an impact on our understanding of its value and worth from a moral perspective? This is especially true in this case, where we are killing a human being. Surely we should have solid grounds for believing this to be a just act, and that part of those solid grounds would reflect our understanding of why we punish people, what we want that punishment to do. As my earlier posts on the matter demonstrate, the death penalty doesn't do all of what we want a punishment to do, and the things that it does do can be done better by other means which do not have the potential to kill the innocent, which would be complete tragedy.