As a former supporter of the death penalty that has come around strongly in opposition, I enjoyed this piece featuring a former prosecutor trying to apologize for falsely sending a man to death row. I loved this line in particular
No one should be given the ability to impose a sentence of death in any criminal proceeding. We are simply incapable of devising a system that can fairly and impartially impose a sentence of death because we are all fallible human beings.
I consider the notion of whether the death penalty is humane or whether we have the moral right to take the life of someone who is guilty of murder to both be red herrings. The key issue for me is that we can't do it fairly and without errors. The appeals process is useful, but can't ever be perfect because often the appeals occur in the same time and place as the trial. Appeals of a black man in 1965 were not of much use, just as appeals of wrongly-convicted day care workers were not of much use in the 1980s and 1990s day care sex scares (even today, Martha Coakely bends over backwards to keep innocent people in jail). Public choice theory tells us government officials have incentives that are different from mere "public service", and we can see that in spades in this prosecutor's mea culpa.
By the way, we can see similar incentives at work in the Jodi Arias trial, where a lot of public hatred was aimed at the one juror who refused to sentence Arias to death. You read in this and other stories that the other 11 jurors were truly angry that they were not allowed to kill her.
The Arias trial also illustrates another issue -- there is a huge gender bias in death sentences. It doesn't get much press, because it hurts men rather than women, but it is really really really hard for a woman to get sentenced to death.