Perhaps both reasons played a part in the 1977 Supreme Court decision; I don't recall the debate about rape convictions being unfairly handed down based on race. I remember the decision only because I was a liberal feminist at the time, (I was 19, young, stupid and highly influenced by my college profs) and didn't believe in the death penalty. But I had mixed feelings because I hated the rapists too! Well, I still think rapists are the scum of the earth, but I have no longer have a problem with the death penalty.
Actually, I am generally against the death penalty, abortion and war. On the other hand I do believe that you are entitled to protect yourself from the attacks of foreign nations.
Dr. Dean (the DNC ghoul in charge) was being interviewed a few years back and the death penalty thing came up. Dean said that as Governor he was immediately made aware of the fact that when you have a convicted murderer (not just one on death row) the odds are very good that if he or she is released, or a sentence is commuted, they are going to kill somebody else ~ and if they are not released, the odds are good they are going to kill a guard or a fellow prisoner.
When it came to the death row guys, he was certain that it was dangerous to keep them around because they ALWAYS kill ~ that is, the probability was 100% with that class of killer.
As a consequence, he changed from a opponent of the death penalty to a supporter of that penalty.
Bet your professors never told you, way back when, about the proclivities of killers to kill.
My alternative to the death penalty is simply the administration of doses of ether sufficient to snuff the "personality" and most of the memory of the killer. Then, keep'em chained up so they can't hurt anyone.