How about:
1) It's been abused, especially along race/class lines 2) It's bloody expensive (~3x more than simple incarceration) 3) There's no evidence to support it as a deterrent 4) It leaves no room for appeal and thus denies due process 5) It's cruel and unusual 6) It's barbaric; aren't we past that? 7) It inflicts punishment on survivors of the deceased who weren't
convicted
Maybe there's more; I didn't give it more than about 20 seconds of thought.
/jordan