Capitol Punishment is not about revenge. Or, at the very least, it's not just about that. Capitol punishment serves three purposes:
-Eye for an eye. Yes, indeed it does. It's restitution. Settling the score. You take a life, you lose yours. That's the deal. You can't give back a life you take, all you can give is yours. It's a neat little social contract, and I'd wager that it works more often than it fails. You take? You give up. That's fair. Don't want to be killed? Don't kill. Neat how fair that is.
-Deterrent, arising from the above. True, people do still murder, but mostly on account of they think they're clever enough to slick it. How many more, we might wonder, elect not to take a human life for fear that they'll lose their own?
-Those who take innocent lives should have something more unpleasant to look forward to than forced early retirement, and we who have not committed their transgression shouldn't have to pay for it.
Oh, and to add to that:
When I go drivin', I stay in my lane.