I think the death penalty has been a big deterrent to crime because even the most vile people have a fear of their own death.
I used to watch the Court TV Channel a lot and liked the Series "Forensic Files" which did a lot of shows on Serial Murderer's and how they were caught. One thing really emerged and that was how many Murder's spilled their guts when faced with the Death Penalty. Yes they were spared because of a plea bargain down to "Life", but by being incarcerated they prevented subsequent murders.
Another benefit from them spilling their guts was that many times to plea bargain down, they had to tell where their victims lay, and many grieving families of the ones the murder's killed, were able to have real funerals and really put their loved ones to rest because of what they said. Without a real threat to them, they would have remained silent and never said where they buried the bodies. What a waste. Victims Families need everything they can in order to move on, in my opinion. If it is the ability to put a loved member in a real grave, with a real headstone, then so be it.
I think you will find, that the threat of given the death penalty, to the ratio of people actually put on death row, is very lopsided. That is, the threat is presented a lot, and has tangible results for society. But just with any threat, it must be carried out once in awhile in order to give it any serious weight. We are a faulty world and an imperfect society, mistakes will happen, but I think as a whole, more good is derived from the death penalty, then the rare, innocent man being executed, from this form of punishment.
Now I say this as a person whose family member was wrongly accused and legally put to death in this country.
God sanctions the death penalty in the bible, even when it is replete with innocent people who are wrongly executed, so who am I to say that it should be replaced with something gentler? More importantly, who are we to say that that it should be replaced with something gentler?
Woe to a society that thinks in its imperfect state, it can find a better system then God's plan on crime and punishment.