There's no undo button for 21 of your best years in prison either. You can compensate -- $20m for example, which is a "partial" undo, but it doesn't undo the harm caused.
The death penalty is barbaric. There is no acceptable argument for it's existence.
A full confession that is never retracted?
What about cases where an innocent person is coerced into thinking they are guilty?
In a world where we accept the Heisenberg uncertainty principle, where does this certainty of guilt arise?