None of these four morally legitimate reasons for punishment includes revenge. Vindictive killing and infliction of pain might make the victim or his relatives feel better, but this goes beyond what is morally justified for restitution and protection. Two wrongs do not make a right. The Bible thus recognizes that any vengeance belongs to God, not to man. Since, as I argue, capital punishment is morally wrong, then to deliberately kill someone, who has already been captured and no longer a direct threat to society, is murder.
Capital punishment gives the government the legal right to commit first-degree murder.
That murder can be proper. But society and government should be nobler and more righteous than a murderer. It would benefit society to amend this vague wording with the more specific prohibition of excessive punishment, including capital punishment, torture, the forced removal or impairment of the human body and its functions, and cruel treatment. Some types of harm are never justified, even for despicable criminals. An ethical government must defend the nobility and dignity of justice.