Supporters of the death penalty might turn this argument on its head, viz. If the death penalty deters, then, by definition, it results in a society in which there are fewer murders than there would be if the death penalty were not invoked. Ultimately, these defenses of opposition are as invulnerable to refutation as they are incapable of persuading anyone who does not already accept their assumption that the deterrence of murders would not justify the use of the death penalty. Indeed, one might ask the opponent of the death penalty just how many innocent people he is willing to sacrifice to avoid executing the guilty. It is those who oppose the death penalty who act out of humane motives.
Motivation is irrelevant to the correctness of an empirical claim.
One such view is that the opponent's opposition flows not from feelings of humanity, but from the fact that the opponent can picture the murderer being executed, while he cannot picture the statistical group of innocent people who will be murdered if the death penalty deters but is not employed. The picture of the execution is capable, as the murder of the statistically expected victims is not, of eliciting guilt and fear of aggression with which the opponent cannot deal. He rationalizes his avoidance of these with feelings of humanity which bolster self-esteem and avoid awareness of his true motivation. It is every bit as reasonable to see this as the opponent's motivation as it is to accept that his opposition flows from his self-proclaimed greater humanity. Like opponents of the death penalty, I too hope that the death penalty does not deter.