It is embarrassing that the most uncompassionate of the Supreme Court Justices are the ones that are visibly Catholic, namely Thomas and Scalia. They dissented, along with Rehnquist, on the ruling regarding putting the mentally retarded to death. Justice Stevens argues that in 20 states, or there about, the practice has been abolished, not counting the states that have banned the death penalty. Stevens' point is that it is clear that the national sentiment and trend is opposed to the execution of the mentally retarded thus making such actions unusual enough to be considered unusual punishment. The dissenters argued that justice cannot be run by opinion polls.

I'm not a lawyer, nor legal expert, but I don't think the intent of the constitution was to create a bloodthirsty system. If anything, it seems the framers wanted to err on the side of caution and were for civility and leniency (ignore slavery for a moment).