The only problem I see with capital punishment is that it is not used often or swiftly enough.
If criminals commit capital offenses (we're not talking about a theft here), and they're found guilty, they should be executed. If they happen to be minors, I guess a lengthier review before sentencing would be in order, but to quote Jules in Pulp Fiction "Well we'd have to be talkin' about one charmin' mfin' pig. I mean he'd have to be ten times more charmin' than that Arnold on Green Acres, you know what I'm sayin'?"
Next step: Joe Criminal was convicted of a capital offense. Your Honor, since Joe has the mental maturity level of a minor, he should not receive the death penalty.