There was a FBi report written years ago, that had studied wrongful convictions that lead to the death penalty. They had concluded at least 20 innocent men had gone to the gallows. I can’t cite this, but I did first read the report from a FR post.
I'd be interested to see that report. It is unfortunate, and it underscores the need to make sure that innocent men aren't executed, but I bet if you counted the number of innocent victims killed by men who were supposed to be in prison for life and committed murders while on parole, the numbers would be staggeringly higher.
Years ago I heard Dennis Prager on his radio show give figures that stated that the average sentance given for murder in the U.S. was 11 years. Based on that, you could make the case that American society really doesn't think murder is that bad. Or at least, the American criminal justice system doesn't think so.
I think that argument is a red-herring. Don’t let the perfect get in the way of the good, so to speak. We don’t demand perfection in any other avenue of life, it pains me to admit. Clearly the law has a long history of siding or erring on the side of caution (at least with any sort of tradition of civilization)
Clearly there are numerous cases beyond count, of known, admitted, convicted psychopaths to keep ole’ sparky busy.