Capital punishment - a curse or a blessing?

Hammurabi's law tells us "An eye for an eye, a teeth for a teeth", so why shouldn't we kill a criminal as a punishment for a murder? Why does this topic divide people in all counties? There isn't something like "vast majority" of adherents or adversaries. The entire society is generally divided into 3 groups. First is "for", second "against" and third- people, who doesn't meddle with politics, society other people's life- they're always covered with a "haze of ignorance" about today's world. The death penalty is the issue, which always pours into media during consideration of some big crime, and then everyone starts to ask questions about rightness of capital punishment. Point of view depends on our experiences. Mr. X can be definitely against the death penalty, but, I apologize for macabre example, if one of his friends or relations was murdered, he would probably want to sentence the guilty criminal for the worst punishment. So after his ordeals he changed his mind.

First and foremost, there is generally the same number of for and against arguments, so we can't decide about being on one of the sides, just by counting.
Adherents' main argument is public security. If you thought that 5-time murderer was set free because his behavior in prison was "correct", went scot-free during the trial or escaped from the jail you would start to be doubtful about your life- running across that guy would probably be a hair-raising experience. Other significant thing is that a criminal would have probably thought twice before committing a crime, if he knew that he could be convicted to death penalty- so this punishment should serve as deterrence. Finally the thing, which is repeatedly mentioned, but is not really pleasant particularly for authorities. The capital punishment is in many instances just economical "way out", if too many taxes go for prisons, the death penalty is initiated.

Adversaries frequently refer to humanitarian feelings and want to stimulate it in adherents. The people who are "against", whatever the circumstances, mention the religion, especially Christianity, which preaches forgiveness, not revenge and in this religion 5th statement of the Decalogue is "Don't kill". Moreover, they remind us that murder is a murder and it really doesn't meter if we do it "legally" or not. And the last but not least, judge is a man and it can happen that, when he look at the evidences he will take the guilt of accused for granted and then, after a year or two, there come new evidences and the truth is, that the man, who was sentenced is innocent. What's then? We can set him free, but if he had been convicted to capital punishment, we wouldn't have had a possibility of bringing him back to life.
Never before have I considered the rightness of capital punishment. It's hardly possible to make up a decision in the nick of time. However, it seems to me that humanitarian attitude is closer to me. I was taken aback when I find out how many of my friends are for the death penalty. I dread thinking about our dubious future, I was trying to convince them, that they're making their upcoming life gloomy, but in vain.
Taking everything into account, all arguments are true and in fact hard to deny. Which of them have real value? We can't even guess the future so I can't imagine what will be the situation in the world in… 2050. We will get to know which of these arguments were definitely important in the future.