CRUEL & UNUSUAL: So, the law now is, it is cruel and unusual to execute the perpetrator of a vicious, premeditated murder who happens to be not so swuft, but it isn't cruel and unusual to lock him up in a cage for the rest of his life. Of course. It's so logical. UPDATE: I'll just quote from Justice Scalia's dissent:

Once the Court admits (as it does) that mental retardation does not render the offender morally blameless, there is no basis for saying that the death penalty is never appropriate retribution, no matter how heinous the crime. As long as a mentally retarded offender knows the difference between right and wrong, only the sentencer can assess whether his retardation reduces his culpability enough to exempt him from the death penalty for the particular murder in question.