In this case, it might be a good idea to use the "sacrifice one for the good of many" analogy. Now, I know what you're thinking; that's communism! But hear me out.
I've studied psychological reports on those who are on death row for murders and raping of children. When these convicts are tested, we have found one common problem; they cannot understand cause and effect. They truly can't. They are given cards, with pictures on them of different parts of a series of events, and told to put them in order. They can't do it! Clearly these people can't separate what they do from the consequences and repercussions of said actions.
These men and women are implusive--they aren't thoroughly thinking through their actions, they aren't "cured" by being in jail, because it's actually a large part due to an underdevloped brain! You may say that they deserve treatment and therapy. First, the brain fully develops at about 22, and the part that recognizes cause and effect registers at about 8, leaving plenty of time to learn right and wrong, and obviously these men and women didn't learn it. Second, you may say that it could be "cured" after years and years of therapy-- so are YOU going to pay for that? It's not even guaranteed successful! I'd say invest in making schools safer, or more security for sex offenders or something.
Even if you can somehow convince yourself that this isn't substantial evidence, let's look at what would happen to them if they were put in jail.
A man commits a crime. He's convicted and goes to jail. Other men around him have committed similar crimes. He spends all of his time around men that think like he does, and begins to assume his thoughts and actions are not only acceptable, but normal! We have almost made this man worse off!
Sure, we can look at it financially--it's a huge burden to us, and let's face it, we have a lot to pay for, out of our own pockets. Selfish as it may seem, who wants to PAY a man (by housing, feeding, cleaning) who killed your neighbor, friend, raped your daughter, or student, or niece? NO ONE. I would go so far as to say that they don't deserve it.
Finally, would it deter murders? I think this is irrelevant. We are talking about justice, and if it does deter others, that's just a plus. As we've seen lately, most people who go out on a shooting rampage kill themselves, and probably want to die if they aren't successful.
The death penalty makes sense because for the safety of thousands, we eliminate one man in the name of justice for another killing. Only in killing others or the raping of a child can killing be justified. That's where the "sacrificing one for the good of many" comes in. It's never good to sacrifice one who is innocent or anything of the sort. It only makes sense to me in the fact that capital punishment is a way to keep many safe.
-Keira
P.S.--I recognize people are very touchy about communism. I'm not suggesting communism be a part of America in any other ways, or that socializing anything would be better. The only ways I agree with socialism is in the ways we already have established; our mail system is socialized for example, and the death penalty can be thought of as a form of communism.