You know, that's an interesting thought.
Perhaps every prison should have an array of options available 24/7: painless poisons, gallows, guillotines, shooting squads, etc.
If any prisoner wants to get out of his sentence, he should have ready access to these alternative exits...
(With all the academics out there wasting tax dollars on "studies," I'd like to see how much tax money such a system would save the US by thinning out the prison population along purely voluntary lines...)
-- KotS