Prisoners are not rehabilitated, they are confined for a set number of years then released out into the population again. Most can't get a job because of their felony convictions even if they learned a trade while in prison. So they usually wind up back in prison within a short time of getting out.
When I die I'm sure to go to heaven, cause I spent my time in hell.
You get more with a kind word and a two by four, than you do with just a kind word.
This is Manu's point too. For the most part, you are correct. We should then look at the goal more and focus on that instead of the current status. You don't win longshot comeback games because you looked at your current status or the "results", you win by focusing on the goal.
If you want to keep them in prison, fine. I have no problem with death for many criminals. Life in prison is waste, both of that life and our dollars. If rehabiliation is the fundamental goal, we should strive for it. No?