mjp - You pretty much narrowed down the challenge of changing death penalty laws to it's essence. It all comes down to taming the blood-thirst and transforming the primal need for vengeance into a more evolved human desire for justice. And yeah, "good luck with that", for sure.
But when you look at how far DNA testing has come (and will continue to improve), it seems we have to re-think applying the ultimate penalty, I think. Once it is carried out, THERE IS NO RE-DRESS OF GRIEVANCES. The state can pay you big money and officially pardon you, and you can write a book/screenplay and make up for lost time if you've been wrongfully imprisoned. But dead is dead and the state cannot try to make good on that, however egregious the miscarriage of justice later turns out to be.
Before anyone perceives me as a "do-gooder liberal" (which I kind of am), let me give you my LARRY HOOVER EXAMPLE of why I am opposed to the death penalty. Mr. Larry Hoover was the founder and "CEO" of The Black Gangster Disciples in Chicago. No need to detail the mayhem he has personally directed over the years, but he has been in prison for a long time and deservedly so. However, inside prison, he has full privileges and rights granted especially for him that virtually no other prisoners enjoy. He doesn't even wear a jumpsuit - he is allowed personal clothing. He has cooking privileges in his cell. And of course, nobody tries to fuck him in the ass. Plus, you can be assured that a portion of those millions of dollars earned in the drug trade by his gang on the streets is waiting in a bank account somewhere. But here's the thing: As good as he has it on the inside, he still wants out. But that can't happen because he is serving life without parole. And I would see that as Win/Win, if every convicted murderer/rapist/monster could be shut away for life, and - simultaneously - there would be no possibility that an innocent man/framed man/wrong man in the wrong place would be put to death. Replace the death penalty with life without parole and it's all good ( to put it simplistically)
The death penalty is the one unique sentence handed down by the courts which cannot be "corrected" after the fact. What's done is done and when the state fucks up (or just railroads you), you are never walking out of those gates with a chance to start over. And good luck with that...