But there are guilty people, people who have committed cold blooded murder - in this case of those they pledged their lives to protect, their own family. Thus - the death penalty.
You still have a problem with that? I remember some 'beach bum' wild-eye (he really was) outside the courthouse, yesterday, approached that chubby gal handing out the free Examiner issue (with the DEATH headline that all the reporters and pundits showed for the camera). He said loudly - I'm OPPOSED to the death penalty. She had about four cameramen surrounding her, trying to get the newsie holding up the headline shot for background. I'm OPPOSED to the death penalty. And some other heavier guy walked right past him and said - Well, I'm in FAVOR of the death penalty, and took his free copy from the gal. It was funny.
I thought all these camera guys, and still-shot guys, who were told to 'mingle' and pick up background that the other guys WEREN'T shooting (I literally overheard one of the producers tell his guys that) would chase after the beach-bum. But he just faded into the crowd. That was it. There was a woman seeking petitions for a parental notification measure, I believe, on the other side of the 'media tents'. But no other I'm OPPPOSED sorts. The local crowd, generally, was not all that opposed, believe me.
If we can be certain, then I could be for it. But because we can not always be certain, I can not be for it, even in the obvious cases of guilt. We are not always smart enough to discern those obvious cases. If we are not able to discern every obvious case, then we leave ourselves open to committing a mistake, putting an innocent person to death. I am not willing to take that risk.
To answer your question more directly, no matter how much the death penalty may seem deserved or how much satisfaction might be derived from putting a murderer to death, that justice or satisfaction is not worth the risk of one innoncent person being put to death. So, in my view, society gives up on execution of even the most guilty in the name of never putting an innocent person to death.
The only other way I see it is if someone wants to argue that our system of justice is infallable or that they think it is okay if innoncent people end up being put to death in the name of condeming true murderers.