> It's simple really - death penalty is permanent, while life imprisonment isn't.
Death being permanent is a feature, not a bug. Is it possible that evil people can continue to negatively influence society from prison? Or even continue to commit heinous crimes in prison? I'd say this scenario happens much more often than killing an innocent.
For example, organized crime. If you don't kill organized crime leaders, they continue to spread their secret oaths among other prisoners and continue to manage affairs even outside of prison via comm links.
I agree that it's bad to kill innocents, but I think with the right policy and rigor, we could make the death penalty an efficient and painless process that has an extremely low false positive rate.
In my mind it's like "yeah, we save the extremely rare false positive at the expense of allowing all the non-false positives to continue to spread and propagate evil for decades"