Why are you opposed to the death penalty? (with poll)

DarkSyde's interesting diary about atheism and some of the commentary there have made me think about the death penalty.  Some suggest that the Democrats ought to go with the high moral position in opposing the death penalty. (I'm using moral in a secular, not necessarily religious, sense.  As an atheist, I consider myself reasonably moral and principled.)  Some have suggested that opposition is a moral position - we are the party of life.  But I don't think that's a winner in the voting booth.  What I do think is that it is possible to convince people to be against the death penalty for practical reasons, even if they believe some people deserve to die.  For example, I oppose the death penalty, but not because I believe in the sanctity of life.  If an armed bank robber kills a bystander during the robbery, then while making a getaway manages to drive into a telephone pole and die, that's fine by me.  Some people deserve to be dead.  But it doesn't follow that society should kill that person.

I was once in favor of the death penalty as a deterrent.  As I gradually learned that it's not an effective deterrent, that data shows that African Americans are more likely to be executed than whites, that DNA evidence has proved retroactively that some people have been wrongly convicted, I changed my mind.  My younger sister was a prosecuting attorney for over a decade.  She took some time off and then became a public defender.  Interestingly, she changed her mind about the death penalty - as a prosecutor she favored it.  Now she opposes it.  

I am interested to hear what other people have to say on this topic - regardless of whether you are for or against.  And your reasons.  The poll has reasons I could think of, but there are surely more.