Of course, this doesn't address the OP, which is not limited to America, and seems to more about the moral status of executing the guilty rather than practical matters such as not executing the innocent.
My answer to
@Jumi would be the same as
@columbus and
@Bob the Unbeliever I find the death penalty repugnant.
Instead, I like the idea of island penal colonies patrolled by boats offshore and fitted with the means to survive such as seed, shovels, plows, livestock, means to fish any lakes or rivers, and the like. Nobody gets off the island once sentenced to it, and nobody that isn't a prisoner ever need go on. If they can cooperate and form a community, great. If they want to kill one another, that's their business.
They can build their shelters, make their clothes, cut their firewood, etc.. No telephones, electric power, Internet, etc., and really no modern technology at all, although others might grant them some medical supplies, radio contact with the mainland, but I'm good with a pre-industrial life for them similar to the early American colonists.
It's pretty fair, inexpensive, and humane, and solves the problem of these people existing without killing them or even caging them.