Where the murder(s) were intentional and depraved, there is close to 0% doubt of guilt, defendant had adequate legal representation and fair trials, and racism wasn't involved, then I can go with the death penalty. But that's a pretty limited subset.
Under those conditions I'm willing to say that a Dahmer, McVeigh, et al. forfeited their right to live. I think there are elements of justice for the victim and their family, some degree of deterrence, partly society taking a strong stand against the taking of another's life, etc. My conditions would place a limit on death sentences, and prevent wrongful cases. I'm okay too with no death penalty, but it is hard to make a case why a Dahmer or a guy who shoots up a backyard barbecue and kills a few people should be allowed to live out their natural life behind bars.