I almost fully (I'll get to my reservations later) support the death penalty. I'll be using murder as an example crime to illustrate my opinion, since its the most serious. Obviously my opinion changes with crimes of a lesser magnitude, but then I'd have to be quite the extremist if I thought thieves deserved the death penalty...although I do think that rapists deserve it as well.
I don't believe that people will contemplate what they've done in prison. If they intentionally murdered someone, they obviously had no regrets at the time, and I think a small part of a person who commits a crime of that magnitude knows that they're eventually going to end up getting caught. If they were going to have regrets, they wouldn't have done it. Giving them a life sentence, to me, is essentially setting them up for life, it's almost a reward for committing a crime. Off our backs, they get to sit in prison for the rest of their lives. How is this fair? I don't think we should have to pay to keep people who we're never going to let back into society out of it. As far as I'm concerned, they forfeit their human rights when they take another's life.
Another thing is that a life sentence is rarely a life sentence. You have to do something that goes above and beyond murder - like, mass bombings or something - to earn a life sentence that actually remains a life sentence, and doesn't get reduced to a pitiful amount of time instead. The death penalty is no more or less than murderers deserve. What right do we have to decide who lives and who dies? Well, what right did they have to make that choice? Why should we treat them any differently? As far as I'm concerned, the moment they take another's life, they forfeit those human rights that they so cling to when trying to stop themselves from getting a life sentence. There are rules in society, and they chose not to follow them. Why should we treat them as a part of society if they're going to break the rules so severely?
The only problem with the death penalty is...well, what if they get it wrong, and execute an innocent person? Our system for administering justice is horribly flawed, and I would say it is incompetent enough to convinct an innocent of a crime they didn't commit, since it is incompetent enough to be lax upon it's sentences. Convict an innocent man of murder, give him the death sentence, then find out a few weeks/months/years later that he wasn't guilty after all...how are you going to break that news to the victim's family? What possible sort of explanation and compensation could you offer them?
Death isn't a punishment either, it's a release. I suppose this view depends entirely on what you think what happens after you die, but killing someone, to me, releases them of any guilty conscience they may have. But then, I don't honestly believe that anyone who commits murder intentionally HAS a guilty conscience, or any sort of conscience for that matter...but if we kill them immediately, how are we going to know whether or not they're suffering because of what they did? But if we imprison them for life, we're essentially setting them up for life. So really, neither solution is perfect.