Speaking as someone who -is- mentally unstable, no, I would not appreciate this. I would prefer someone just execute me if I ever went that far off the boat.
As for those that would argue that I waived those rights via committing those violent, heinous crimes in the first place? Well, if you sink to -my- level and destroy me, brainwash me, etc, than you're no better than I am. I would "win" proverbially by forcing you to become a monster like me in order to defeat me.
Plus, on top of this, no matter how good technology gets,
people will still make mistakes or even intentionally fib reports created by machines. What if we sentence an innocent man to be reprogrammed? Could you imagine or live with the horror of not only destroying a person's loved one, but to then tell them "we're sorry that your loved one is a zombie." Plus, the moment we justify this, we can start justifying it for more and more extreme things.
This would go to ugly places, very quickly, and would be too morally questionable to ever put into practice without doubts lingering behind about it. This is, of course, assuming that the process is 100% perfect and NEVER backfires, too.
EDIT
@Christiefries: You believe in the immortal soul, yet you also believe in reprogramming people whom don't "fit"? Isn't that a little... Odd? Contradictory, even?