On Murder.
actually, "retzach" (both Exodus 20:13 and Deuteronomy 5:17) translates to closer to "murder" then to "kill."
The significance of the difference is quite high. Capital punishment is not murder, killing a opponent in wartime is not murder, killing in defense of self/family is not murder.
It's quite unfortunate that Christians and Catholics have proven time and time again their propensity for inaccurate translations. I think maybe they should start requiring their members to learn the original languages of their holy works, like the Jews do.
http://www.jewishvirtuallibrary.org/jsource/Bible/Exodus20.html
http://www.jewishvirtuallibrary.org/jsource/Bible/Deuter5.html
But I suppose the arguement could be made we are talking about Christians, not Jews, so I press must press on.
Despite Martin Luther's use of the "kill" translation, his interpritation of this section is fairly inline with how I would read it:
"We have now completed both the spiritual and the temporal government, that is, the divine and the paternal authority and obedience. But here now we go forth from our house among our neighbors to learn how we should live with one another, every one himself toward his neighbor. Therefore God and government are not included in this commandment nor is the power to kill, which they have taken away. For God has delegated His authority to punish evil-doers to the government instead of parents, who aforetime (as we read in Moses) were required to bring their own children to judgment and sentence them to death. Therefore, what is here forbidden is forbidden to the individual in his relation to any one else, and not to the government." (http://www.iclnet.org/pub/resources/text/wittenberg/luther/catechism/web/cat-07.html)
With the implied extension that, when acting as an agent of the government it is not forbidden, this is a reasonable interpretation. Martin Luther doesn't directly address matters of self-defense, which one may conclude puts it in the realm of the proscribed, an interpretation (of the original work, not Martin Luther's commentary) I would reject.
So too with Matthew Henry's Interpretation:
"The sixth commandment concerns our own and our neighbour’s life (v. 13): "Thou shalt not kill; thou shalt not do any thing hurtful or injurious to the health, ease, and life, of thy own body, or any other person’s unjustly.’’ This is one of the laws of nature, and was strongly enforced by the precepts given to Noah and his sons, Gen. 9:5, 6. It does not forbid killing in lawful war, or in our own necessary defence, nor the magistrate’s putting offenders to death, for those things tend to the preserving of life; but it forbids all malice and hatred to the person of any (for he that hateth his brother is a murderer ), and all personal revenge arising therefrom; also all rash anger upon sudden provocations, and hurt said or done, or aimed to be done, in passion: of this our Saviour expounds this commandment, Mt. 5:22. And, as that which is worst of all, it forbids persecution, laying wait for the blood of the innocent and excellent ones of the earth" (http://www.biblestudytools.com/commentaries/matthew-henry-complete/exodus/20.html)
He includes the things that lead up to murder (which basically can be summed up as the majority of the "seven deadly sins"), as murder. I don't know if I can accept that, but I understand certainly understand it. It's worth noting, again, the emphasis is on murder, not killing (A distinction which is made clear) in this commentary.
I think maybe your interpretation of capital punishment as proscribed and therefore hypocritical for a Christen is wanting.
All that said, I am opposed to capital punishment, my reason has nothing to do with religion (catholic, jewish, or otherwise). I just have a problem with the poorly made psudo-religious arguments on this topic.