I'm not particularly sure why, but the main thing usually said to me is "we have no right to condemn someone to death". This is the usual reason I hear for not supporting the death penalty, but it's ludicrous. The murderer obviously believes they have the right to condemn someone to death. Are others suppose to be "above" him and not stoop to his level? Yeah, whatever. Maybe I'm just one of those guys who don't like living alongside those kind of people.
Of course, many have also critized the Republicans for supporting the death penalty while being pro-life. Um, HELLO? You're comparing the murder of a BABY to the murder of a MURDERER! Notice the difference? Man, King Solomon must be rolling in his grave to hear a bunch of self-righteous assholes say shit like this.
The only appropriate penalty for being a gang member. Crips, Bloods, Pachucos, and other gang members never mug another chump after capital punishment.
To the main point: Why do some liberals oppose the death penalty?
A) It's very, very expensive. Yes, a lot more so than just shoving the bastard in prison for the rest of his life. Huge pull on our tax dollars
B) The number of people who have been wrongfully convicted, sentenced to death, and then found to be innocent is disturbingly high.
C) Statistically, minorities are far, far more likely to be put to death largely because of preconceived biases among the jury. Also, poorer minorities have to deal with shitty public defenders that can't put forth a good case, unlike far wealthier white criminals who can hire the best of the best.