This has probably already been said at some point in this epic thread, but I think Jesus made it clear what we should do with old testament calls for the death penalty. With the woman caught in adultery he said "let the one without sin cast the first stone". Because none of us are without sin, none of us have the authority to condemn anyone to death. Only Christ does. And he said to the woman, "Does anyone condemn you? (No)... Then neither do I".
This has been addressed, actually. What you're missing is that this story isn't and never was intended to address the death penalty at all. Rather, if it addresses anything other than yet another instance of the pharisees trying to catch Jesus in a trap, it addresses justice. Specifically how laws are justly to be enforced.
It ain't by stone-wielding mobs in the street. Which is what those people in that story were. There was no judge and Israel had no authority to enforce that law even if there had been. They were under Roman jurisdiction and the Roman forbade any death penalty enforcement by anyone but themselves.
For Christ to have condoned that woman's stoning her guilty would have had to be established in court, before a judge, by the witnesses. And the man involved would have been facing judgment as well. Then her stoning would have been just and in accordance with Mosaic law. The same law Christ Himself gave to Israel in the first place. Still wouldn't have been legal under Roman law, though.
What this story illustrates is not the just enforcement of Mosaic law but a stone-wielding mob of vigilantes intent on murder.
But if you want to argue all that, then try this first. If the death penalty was done away with here, in this one instance, without it ever actually being addressed...what about Romans 13: 4?
Romans 13:3-5 (New King James Version)
3 For rulers are not a terror to good works, but to evil. Do you want to be unafraid of the authority? Do what is good, and you will have praise from the same. 4 For he is God’s minister to you for good. But if you do evil, be afraid; for he does not bear the sword in vain; for he is God’s minister, an avenger to execute wrath on him who practices evil. 5 Therefore you must be subject, not only because of wrath but also for conscience’ sake.
What does the "sword" there refer to? Does a sword do
anything other than kill? What does "execute wrath" mean, following immediately after the reference to that sword? This doesn't clearly establish not only the government's God-given duty to enforce the law but to do so with the "sword"?
Even if you hold fast to the tired traditional understanding of John 8:1-11 you still have to explain how Roman 13:3-5 can follow well
after that event and yet not uphold the death penalty.