True, it does not use the word retribution; instead it uses the word vengeance. These words in this usage are synonyms.the punishments inflicted by the civil authority, which is the legitimate avenger of crime…
Are you suggesting that retribution is not a valid objective of punishment, or that the concept of punishment is somehow different for capital punishment than for all other forms?
Yes it does; protection is a surely a benefit of punishment, but acknowledging that it is a benefit does not at all mean that it is the primary objective. Punishment can also provide deterrence as well as rehabilitation, but, like protection, they are desirable outcomes. They are not the primary objective.
Cardinal Dulles who you have quoted from often, makes it clear as a bell how we are to understand the concept of retribution within human justice.
*"In principle, guilt calls for punishment. The graver the offense, the more severe the punishment ought to be. In Holy Scripture, as we have seen, death is regarded as the appropriate punishment for serious transgressions. Thomas Aquinas held that sin calls for the deprivation of some good, such as, in serious cases, the good of temporal or even eternal life. By consenting to the punishment of death, the wrongdoer is placed in a position to expiate his evil deeds and escape punishment in the next life. After noting this, St. Thomas adds that even if the malefactor is not repentant, he is benefited by being prevented from committing more sins.
Retribution by the State has its limits because the State, unlike God, enjoys neither omniscience nor omnipotence. According to Christian faith, God “will render to every man according to his works” at the final judgment (Romans 2:6; cf. Matthew 16:27). Retribution by the State can only be a symbolic anticipation of God’s perfect justice.
For the symbolism to be authentic, the society must believe in the existence of a transcendent order of justice, which the State has an obligation to protect. This has been true in the past, but in our day the State is generally viewed simply as an instrument of the will of the governed. In this modern perspective, the death penalty expresses not the divine judgment on objective evil but rather the collective anger of the group. The retributive goal of punishment is misconstrued as a self-assertive act of vengeance."*
You keep saying that retribution is the primary end of justice. Clearly Cardinal Dulles explains that although God has the power to redress the divine order of heaven and earth… mere humans not being capable of knowing the soul of the person or the nature of its affect on the divine order… is limited redressing the human order ie. the good of the relationship between between men. This we call the common good. Aquinas…
“Justice, as stated above (Article 2) directs man in his relations with other men. Now this may happen in two ways: first as regards his relation with individuals, secondly as regards his relations with others in general, in so far as a man who serves a community, serves all those who are included in that community. Accordingly justice in its proper acceptation can be directed to another in both these senses. Now it is evident that all who are included in a community, stand in relation to that community as parts to a whole; while a part, as such, belongs to a whole, so that whatever is the good of a part can be directed to the good of the whole. It follows therefore that the good of any virtue, whether such virtue direct man in relation to himself, or in relation to certain other individual persons, is referable to the common good, to which justice directs: so that all acts of virtue can pertain to justice, in so far as it directs man to the common good. It is in this sense that justice is called a general virtue. And since it belongs to the law to direct to the common good, as stated above (I-II, 90, 2), it follows that the justice which is in this way styled general, is called “legal justice,” because thereby man is in harmony with the law which directs the acts of all the virtues to the common good.” - Summa Theologica, Justice
Human justice/retribution/vengeance is
symbolic of Gods justice/retribution/vengeance if it is directed to the common good. That is, if it directed to the good of the relationship between men within the community of their belonging. If God says death is the dessert of murder, man not being capable of seeing either the state of the soul nor the divine order… is limited to acting for the good of the community it serves when addressing crime. This encompasses many aspects to determine the gravity of the crime against the community and the type of redress that will best serve it for the good.