I think that Turbo has effectively shown the errancy in theo's arguments, and indeed some unintended hypocrisy, in theo's answers, to some of Turbo's carefully worded questions.
I would advise him to abandon his line of reasoning, that forgiveness is only equivalent to having the government neglect its authority, by substituting corrective imprisonment, for the death penalty, in cases of capitol crime, at the behest of repentant Christians, who understand the Gospel.
I like Turbo's statement that it might even be the greater evil to intentionally withhold the death penalty then it was for the original murder done in the heat of the moment, perhaps.
When I counsel young women who are about to abort their babies, I often say something similar. Maybe you never intended to get yourself pregnant, or even planned to have sex. But you are intending to, and have intentionally planned the death of your baby for today. This is far worse, then any thing you have done up to now. Please turn around and repent, now!
I agree wholeheartedly with the idea that if the death penalty were swift and severe, murder in this country would be minimal. Therefore the greater evil is what the government has done, in not having one, or enforcing one!
If I were theo I would move on to King David, the woman caught in adultery, and "it is His Kindness that leads us to Repentance." To mention just a few. That would be a better line of reasoning, in my eyes at least.
As an aside, and even though I know most people think that the Law has been entirely done away with, it was legal in Israel for a brother to kill a man who accidently killed his own brother; Either before he reached a city of refuge, or after he was found innocent of voluntary manslaughter by its judges, if he stepped foot outside of its boundaries. There was no need for a stoning of the "manslaughterer" or of the "brother" who may have killed him with his bare hands. It was entirely a personal and "non governmental justice system and issue.
That case would surely drive todays non death penalty advocates to fits.