Even reasonable doubt isn't perfect, even when due process is strictly observed. And then there are cases like Rodney Reed, on death row for murdering the ex-fiancee of the cop who arrested him and told a fellow police academy student if he ever caught his GF cheating he's strangle her with a belt to avoid fingerprints (his ex was strangled with a belt, of course. ) They found DNA evidence from the investigating officers on beer cans from the murder scene, the dudes public defender slept through part of the trial, and his appeal was rejected on the grounds it was filed one day past the deadline. I'm not saying he's innocent, just that I'm not comfortable executing him. Though I'm more comfortable than I was before the ex-fiance of the murder victim was kicked off the Georgetown police force for arriving at a domestic disturbance and then kidnapping the woman present (at gunpoint) driving her somewhere else and demanding sex.

There are innocent people in prison; we might not have reason to doubt in particular cases, but in others we have ample reason to doubt and they remain in prison. That's yet another reason to treat convicted criminals like human criminals rather than a disease to be eradicated. Which applies to the con whose done his time, but it often doesn't work that way in practice. Keep prisoners away from the society they threaten and supervised, treated decently but not luxuriantly.