It's not. You're not getting the point.Why? Appeals process can exonerate an innocent person from death row, and innocent people can die serving a life sentence.
Why is a the death of an innocent lifer (or even an innocent someone who dies while serving a short term) less devastating and more acceptable than a wrongful execution?
Here's how it works:
Let's say that, on average, death penalties are carried out several years after conviction, giving time for appeal. Life imprisonment sentences also allow appeals during the same period, so we can cancel this out as common to both options.
So... assuming the prisoner is innocent, what are the chances of exonoration and release beyond the point that the death sentence would be carried out?
Case 1 - death penalty: 0. The guy's already dead.
Case 2 - life imprisonment: some non-zero value. Let's call it 'X'.
This means that the cost in case 2 is as follows:
- D is the probability of death in prison
- L is the value of a life (or the cost of a wrongful death)
- X is the probability of exonoration before dying in prison (what I mentioned before)
- Y is the value of a year (or the cost of a year in prison)
- Z is the number of years from when execution would've occurred until release
The expected cost of a life sentence of an innocent person for the period beyond when an execution would've occurred is:
Ex(life) = DL + XYZ
D = 1 - X (since these are the only two options), therefore
Ex(life) = (1 - X) L + XYZ
= L - XL + XYZ
= L - X(L - YZ)
Compare this to the expected value of the death penalty:
Ex(death) = L
So...
The difference between them, i.e. the difference in cost of life imprisonment vs. the death penalty, is:
Ex(death) - Ex(life)
= L - [L - X(L - YZ)]
= X (L - YZ)
IOW, when a person is wrongfully convicted, we can expect less cost in human suffering as long as:
- there's any chance of exonoration and release whatsoever, and
- the time spent in prison presents less of a human cost than death.
I hope that even you can admit that the first point is true.
And since I've never once heard of a wrongfully convicted person complaining that he wishes he had been killed (including Steven Truscott, who spent nearly 50 years in prison for a crime he didn't commit), I'd say that the second point is true as well.