"From this day forward, I no longer shall tinker with the machinery of death. For more than 20 years I have endeavored - indeed, I have struggled - along with a majority of this Court, to develop procedural and substantive rules that would lend more than the mere appearance of fairness to the death penalty endeavor. Rather than continue to coddle the Court's delusion that the desired level of fairness has been achieved and the need for regulation eviscerated, I feel morally and intellectually obligated to concede that the death penalty experiment has failed."