The state derives its authority to kill from the same place it does to regulate pharmaceuticals. We have a legal framework within which such things are allowed (I don't argue that the dp is illegal, just ill-advised), and we have a citizenry that wishes those things done.
But some of the things the state does, though legal, are ill-advised. I believe the death penalty falls into that category. I'm not a bleeding heart -- there are a lot of guys on death row I'd be happy to execute personally. But this is not about "feeling good". For me, it's about what works and what doesn't. And, if anything, I believe the death penalty, paradoxically, brings on more of what it is we seek to prevent.