That's a philosophical point. In most areas of legal justice, the penalty exacted for transgressions far exceeds the damages. That is to say, the man who steals a hundred dollars or who punches someone in the face loses far more value from his life as punishment than he caused someone else to lose. A life for a life is a rather mild punishment compared to the rest of the justice system, especially considering the death penalty is typically meted out for multiple brutal murders, often preceded by torture and rape. A just world would have these monsters subjected to the same nightmare to which they treated the innocent.

However, I agree with Paul. The fact that anyone not guilty of the crime is executed is unacceptable, to say nothing of the startlingly bad accuracy of the system in practice.