The current problem with the death penalty is that it is used so sparingly that we do not know if it's a deterrent or not.
We know it's not a deterrent in itself. We also know our criminal justice system is incapable of being trusted with such a significant responsibility. We know that every time we take a look at convictions at any level be it misdemeanor or capitol we find a (to me at least) frightening number of inappropriate sentences and convictions.
We find an unacceptably high ratio of instances where the cases brought against dependents are lousy with misconduct and incompetence by those that we trust to carry out the responsibility of fair and impartial justice. The fact that we chose to close the books on those already executed and subsequently deny them any potential for exoneration is not relevant. It's a cowardly method of evading the central issue most of us (I believe) really have with capitol punishment. It is an appropriate sanction for those who have earned it but with the way we run our courts, in far too many cases, it's impossible to tell if the conviction has any real merit.
The idea that we just recently started to convict the innocent is obviously what many would like us to believe.
Many will point to the occasional case where a defendant has made confessions (assumingly without duress), or is faced with incontrovertible physical evidence that establishes guilt. As if it justifies the "occasional" miscarriage of justice.
We know that we can not trust our courts. Right here on this board there's a plethora of rants questioning the abilities and motivations of those we entrust with our best interests. Only when the "authorities" pander to our own personal agendas do we find ourselves in support of their actions. We ignore the cases where unreliable "expert" testimony, lab results, investigative methods and official misconduct have been proven. As if these are rare occurrences that somehow slipped through the cracks of an otherwise reliable system. I personally believe they are the norm. Our criminal justice system has become a criminal justice industry and it will do anything in it's power to perpetuate itself. Like all industries where accountability and integrity are given less priority than "efficiency".
It is in fact a proven that when apprehension and conviction is reasonably assured there is a decrease in the instance of every category of antisocial behavior. When somebody is fairly sure they will be caught, they rarely commit. Maybe it's time we entered the 21st century and brought all of our current resources to bear in a way that would help us help the criminal justice community serve our interests more in keeping with their fundamental mandate.