My friend Paul Manata attempts here to reconcile the Augustinian belief that God creates and ordains all things for his glory, including the deservedly eternal damnation of some sinners, with the principle that one ought never to treat other human persons as mere means.
He appeals to a modified version of the Kantian principle, according to which we must only treat other persons in ways to which they could rationally accept. His suggestion, drawing from a line of argument I have used against Jerry Walls, is that God could give adequate evidence to those who are in hell that their suffering and punishment is for a greater good, namely the greater good of the demonstration of God's justice for the benefit of the elect. He suggests that the damned could in principle rationally consent to their punishment on these grounds, and thus God does not treat them as mere means in an objectionable way.
You can't say Paul isn't clever. Still, I think there are some problems with his argument. Some comments in response:
First, I agree that there need not be any conflict between these two affirmations; God ordains and does all things for the sake of his glory, which means for the demonstration of his character for the felicity of those who know him; God never treats human beings as mere means. The problem only seems to arises if we suppose that a part of God's character is this commitment to retributive justice, and furthermore that retribution for sin requires an infinite, unending punishment.
Theodore of Mopsuestia and Diodore of Tarsus, appealing to Luke 12.47-8, argued that those in hell will be punished to various extents in keeping with the desert of their sins. They did not suppose that sin against God demanded unending punishment, and so they envisioned that sinners would eventually leave hell and reconcile to God. They can affirm that God has a commitment to retribution, that he treats persons according to their deserts, and nevertheless all are saved because no one could deserve infinite punishment.
I say that the problem only seems to arise because Christ's crucifixion and resurrection seem to provide a counterexample. There are some textual reasons to suppose that Christ's own death involved suffering the eschatological punishment of God: he warns, for instance, that sinners will be cast into the outer darkness whereas Christ suffers outside the city as darkness covers the land, after which he cries out in a sentiment of abandonment. Yet Christ, suffering this eschatological punishment, was nevertheless raised from the dead afterwards. Perhaps it is the same way with sinners in hell. Origen cited Ps 78.34: When he killed them, they sought for him; they repented and sought God earnestly. It might be that those in hell suffer infinite punishment in some temporally limited amount of time, that they are "killed" somehow, after which they are restored to life. Origen cites the example of Paul: the informant, accuser, persecutor is killed and the apostle of Jesus Christ is brought to life.
Second, I think there is a problem with the modification of the Kantian principle to which Paul appeals. There is an ambiguity in the word "could." Paul grants for the sake of argument that God only treats persons in such a way as they could rationally consent to being treated. Thus, God could convince those persons in hell that their damnation is for a greater good, and the damned could rationally consent to being damned. But how do we understand this "could"? They could if they were ideally rational, or they could granted the character and dispositions that they actually have?
Sin in the New Testament is largely characterized by inordinate love of self: idolatry, greed, adultery, hatred, unforgiveness, licentiousness, etc. On the other hand, the characteristics of the person in whom the Holy Spirit dwells and who has the wisdom from above are paradigmatically selfless and self-sacrificing and concerned for the other: gentleness, peaceableness, kindness, willingness to yield, mercifulness, patience, etc. For a damned sinner to consent to being damned for the felicity of the elect seems to require a selflessness as could only be had by someone in whom the Spirit of God dwelled, thus compromising her status as damned. I think it implausible, indeed impossible, to suppose that a damned person, sinful as she is, could consent to being damned for the greater good, given her actual character.
On the other hand, I don't know what an ideally rational agent would do, and probably neither does Paul, because we haven't seen one. My impression is that it is never rational to engage in ultimate self-sacrifice without some kind of promise or hope of reward or subsequent restoration (which would not make it ultimate self-sacrifice). Even Christ gave himself for our sins knowing that he has the power to take up his life again once it has been taken from him. So I am doubtful that the damned, if ideally rational, could consent to being damned for the greater good.
But more importantly, I think that this variation of the Kantian principle fails to capture its essence. We have to treat people to a great extent as we find them, not as they could be. Suppose a fat man could, if ideally rational, consent to being pushed off a bridge to save the lives of five other men on a railroad track below. As things actually stand, however, he would not consent to being pushed, because he loves his life too much to do such a thing. I think pushing him and attempting to justify your act by appeal to Paul's modified Kantian principle would be unconvincing at best and downright malicious at worst. To a great extent, it is necessary for us actually to acquire the consent of those whom we intend to use as means. Yet Scripture nowhere envisions that God will actually get the consent of those persons who are in hell; on the contrary, by my lights, it paints the picture that they'd like just as soon to get out (e.g., Mt 25.11-2).
On the other hand, I think it would be immoral to use someone as a mere means to an end from which they could not benefit, even if they rationally consent to being so used. It would be immoral to kill and eat the organs of a person, even if she rationally consented to this and even wanted me to do it. In this case, there is a lack of respect and reverence for the human person. I think human persons are valuable, so much so that we can neither use them as mere means to an end from which they cannot benefit, nor may we offer ourselves up to be used as mere means to an end from which we cannot benefit. Doing this would display a lack of respect for ourselves. Of course, self-sacrifice is possible and even demanded by God, but God simultaneously promises reward for those who do what he asks. The self-sacrifice is not ideal but necessary to reflect God's character or to accomplish his purposes in the present state of things.