Let me start by saying that I am a liberal/progressive who supports the death penalty. Not in a hypocritical, knee-jerk, right-wing nut-job, who-would-Jesus-kill kind of a way, but in a well reasoned, liberal/progressive sort of way.
I imagine I might take some heat for this position. There are likely some dKos members who don't believe you can be both. So be it. But here are the reasons why I, as a liberal/progressive, support capital punishment.
It begins with our social contract. We all agree to live in a society together abiding by certain rules. These rules protect me from you and vice versa. There are some who argue "I didn't agree to anything, I was just born here". Well, you could always leave. And if you vote, you're exercising your role in that society. You are taking an active role in deciding the rules of the social contract that we all are expected to abide by. Under these rules, the ultimate crime is taking another life. The appropriate punishment for the ultimate crime (the majority has deemed) is the ultimate retribution, forfeiting one's own life.
Is killing someone as punishment for murder a "moral" act? Is it the "right" thing to do? The answers reside within you, your heart, your soul. But your answers are not MY answers. And if you oppose the death penalty, your answers to those questions are not the same as the majority of Americans. Like it or not, we have agreed that majority rules (within the parameters of the Constitution).
The main question is simply this: Is it EVER appropriate to kill another human being? If you consider war, self-defense or a similar kill-or-be-killed circumstance, the answer is clearly yes. So, the issues is not WHETHER it is correct, but under WHAT CIRCUMSTANCES it is correct.
I will concede that innocent people have been sent to prison and there is a likelihood that some have been put to death. That is a tragedy. It should never happen again. But that doesn't mean that the death penalty is the problem, it is the criminal justice system that has flaws. And those are being fixed with new technology that can say with certainty that who actually committed a given crime. Personally, I would not condemn someone to death without DNA evidence (or similar scientific proof) that proved with absolute certainty that the accused was guilty. Some might ask "how can you know with certainty that the accused is actually the killer?" Well, how do we know anything with certainty? How do I know that the act of typing this post isn't just the result of oompa-loompas pumping my head with strange and fantastic drugs and my entire "reality" isn't just the product of Willie Wonka's whimsy? I don't. But I am reasonably CERTAIN that it is not.
Justice in this country is supposed to be blind. Race, class, gender, etc. should not be a determining factor in someone's guilt or innocence, but it is possible that in some cases those issues play a role. Jurors are human, inherently flawed, prone to mistakes, subject to whimsy and emotion rather than reason and rationality. But this system is better than any other I can imagine. We have an appellate process to address questions about the system. It takes years and sometimes decades. After years of rehearing and re-evaluation, the process gets as close to the knowable truth as humanly possible. Those who have been wrongly convicted and subsequently freed are the direct result of this process. That is the system working. And when the death sentence is carried out, that is the system working as well. No one goes to the death chamber without an exhaustive review of their case (expect maybe in Texas, where the have a conveyer belt in the death house).
The death penalty may seem archaic or barbaric to some. They have higher hopes for humanity than I do. As long as there are those among us willing to kill, there must be an appropriate response from society. I just accept the fact that there is a blood lust within all of us. It is only a question of what it takes to reach that boiling point.
There are those who will say "the death penalty is not a deterrent," as if that is the sole rationale for its existence. I find the notion that you could even try to measure that statement rather silly. If you talk to the killers about it, they weren't deterred. That's why they are killers. Can we possibly know HOW MANY murders never took place because the potential killers were deterred by the possibility that they might take a ride on "Ole Sparky?" It is like trying to prove a negative, it cannot be done. So the deterrent quality of the death penalty can never be adequately measured.
I won't get into the other benefit of the death penalty as a tool for prosecutors to extract guilty pleas from killers who are afraid of the death chamber.
In closing, Stanley Williams has been put to death at San Quentin. I agree with this act. I would be lying however, if I didn't admit there is a part of me that wishes it were unnecessary. How I wish that there were no need to kill in order to prevent/punish killing. But that isn't the world we live in yet.