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.
The only appropriate penalty for being a gang member. Crips, Bloods, Pachucos, and other gang members never mug another chump after capital punishment.