Capital punishment is to the whole society what self-defense is to the individual. The Ethics of Life and Death J.P. Moreland, p. 115. C. Objections to retributionism 1. Arguments that prove too much. Many arguments against capital punishment prove too much because they apply with equal force against any punishment at all.
Capital punishment is applied unfairly.
Even if this were true, the injustice here applies to those that got away, not to those that got punished. The injustice is remedied by applying it more often, not less. Better unequal justice than no justice at all. You don't take away what the first man deserves, withholding his pay because the second man didn't get paid. That would double the injustice.