As more states abandon the death penalty (as much for economic reasons as moral ones), Andrew Gelman poses the critical question for death penalty supporters (still a majority, as he notes):
My larger perspective on the death penalty, informed by my research with Jim Liebman several years ago, is that you can only accept capital punishment if you’re willing to have innocent people executed every now and then. And, the more effective you want the death penalty to be, the more innocents you have to execute.
The occasional execution of innocent people might be deemed ok in some settings—-they shoot deserters in wartime, and if a country is in the midst of a big enough crime wave, I could see people accepting the need for the occasional lethal mistake of the judicial process. My point here is just that if you want to execute people on a regular basis, you’re gonna make some mistakes. We saw this in our research on death-sentencing reversals, which were not merely the actions of a few liberal court panels.
And for me, executing an innocent person is far worse than not executing a guilty one.