I can recall a study done about ten years ago about a group of young, violent offenders being sentenced to a type of 'boot camp' punishment. The results of this were that the offenders, after having completed the program, were very fit and much more organized criminals than they'd been when they entered the program.
As for capital punishment, I've always believed it's the mark of a "civilized" society and its government not to condemn people to death. While it's the case that barbaric individuals do exist, institutions that deal with them should never stoop to the same barbarism, no matter how 'humane' it might be said to be. If killing is against the law then the State should not be above the law. It's a hypocritical double-standard if it is.
I know there can be a lot of 'what if it happened to you?' arguments in favor of capital punishment, and I can't answer that except to say I'd hope my convictions would stand in the face of such tragedy. What I can say by way of answering is a friend, many years ago, had an infant that died from Sudden Infant Death Syndrome. Her husband came home to find her sitting alone in the kitchen - her baby having died hours earlier in the day. It was a terribly traumatic moment made worse by the fact the police, when they were eventually called, were of the opinion she had murdered her own child simply because she didn't immediately phone them to report the death. This kind of ignorance of the grief a mother suffers could well have resulted in her being charged and possibly convicted of a crime that carries the death penalty in some places. The point I'm trying to make is the State law institutions, as institutions, simply don't have the capability to judge correctly in all situations. This alone is reason enough (for me) to not support capital punishment.