Contd: The death penalty is justified in 3 ways that I know of off hand:
1) as a deterrent to committing capital crimes
2) as an appropriate social consequence for capital crimes
3) as a form of revenge by the society for certain kinds of crimes
To be an effective deterrent, it must be widely perceived as a likely consequence of committing a capital crime, and the way our courts currenty use it, this is not the case; so the 1st reason is out. I personally don't believe in social revenge, in principle, so I don't agree with that one, but that's a personal opinion. There remains the idea that it is an appropriate consequence for crimes like taking another's life. That argument hasn't been effectively challenged yet.