I'm going to comment on this:
i) It may be a mistake for me to respond. I disagree with Piper's position. Someone like Bnonn Dominic Tennant, who's more sympathetic to Piper's position, might be better equipped to defend it.
Likewise, I'm not deeply conversant with Piper's theology. My reading of Piper is quite limited. I can't vouch for the accuracy of Adam's interpretation, or whether Piper has said things elsewhere which would bolster his position.
ii) One initial problem is that Adam is basically operating with philosophical theology whereas Piper is basically operating with exegetical theology. For Piper, the two wills of God is a revealed truth. For him it doesn't ultimately matter if that appears to be inconsistent to our finite minds.
iii) Jeremy Pierce has been critical of how Piper parses God's self-glorification:
iv) Conversely, I've argued that it's not ipso facto incoherent for the Calvinist God to have unrequited desires:
So with those caveats duly register, let's proceed:
- If the doctrine of Unconditional Election is true, then God prefers that not all be saved.
- But the Bible says that God prefers that all be saved (1 Tim 2:4, 2 Pet 3:9, Ezekiel 18:23, 32).
- Therefore, the doctrine of Unconditional Election is false.
How might the the defender of Unconditional Election respond? One might deny  by some method of interpretation that concludes that the verses in question do not really say God prefers that all be saved.
That's my own position.
Piper’s response is simple: the argument equivocates the meaning of the word “prefers.” In  God prefers to actualize states of affairs that do not entail the salvation of everyone; in  God prefers that the states of affairs in which everyone is saved were actual. In the first sense, God prefers to actualizes something; in the second, God prefers that something else were actual. A nice way of putting it (borrowed from Steven Cowan) is that all things being equal, God prefers to save everyone, but all things considered, God prefers not to save everyone. Think of a physician who intends to help people overseas ward off a deadly disease, but upon hearing that his homeland is being impacted by the disease, he decides to stay and help his own people. It is perfectly coherent to understand his conflicting preferences in this way. And it is this sort of “two wills” theology that is unavoidable when trying to answer the problem of evil.
On the face of it, that's a coherent position.
Let us suppose this is right. Then, we have to answer this: what sort of consideration is it that so constrains God from saving everyone? What is at stake for God if he fails to save everyone? Piper’s answer is that God’s glory is at stake: God would fail to maximize the revelation of his glory to the elect by virtue of failing to send some sinners to hell so that they might bear, and in so doing reveal, the full weight of divine wrath. Piper believes that a world where this sort of wrath is not actualized is on the whole less preferable than a world in which it is actualized (alongside a display of mercy), because it fails to exemplify the sternness of God’s wrath.
Hovering in the background of this discussion is the assumption that there's one best possible world. That one possible world is simply preferable to another possible world.
And no doubt there are cases where that is true. Some possible worlds are clearly worse than others.
But in other cases, that's simplistic. One possible world may be preferable to another in some respects, but less preferable in other respects. Among the better possible worlds, each has a unique package of goods that isn't captured by the alternative.
I have three objections to this consideration. First, it imposes a rather strong limitation on God’s freedom in that He is not really free to show mercy to whomever He likes. Piper elsewhere assumes that the failure to uphold God’s glory is a moral failure (see The Future of Justification, 64).
i) There's a potential equivocation here. Does Adam mean a moral failure on God's part, or on the part of humans?
If the former, then I agree with him that Piper's understanding is flawed in this respect. If the latter, then Adam's conclusion is fallacious.
ii) Keep in mind, too, that if God has a goal that's inconsistent with universal salvation, then God can't save everyone consistent with that goal. That's a contingent limitation. God can save everyone minus the goal. Or God can achieve his goal. It's the combination that's impossible.
To put this in reverse: if it's God's goal to save everyone, then God can't damn anyone. But that's not a strong limitation on God's freedom. That just means God can't perform a pseudotask. Not all possibilities are compossible. God can't pursue contradictory goals, that's all.
A second objection grants the truth of the penal substitution theory of the atonement and argues that the fullness of God’s wrath could be sufficiently displayed (if it must be displayed) in the work of Christ. The elect would need nothing more than the cross of Christ to understand the depths of their sin and the severity of God’s response to it. But if a populated hell is required to sufficiently display God’s wrath to the elect, then the cross of Christ is insufficient to display God’s wrath to the elect.
i) That's equivocal. The primary purpose of penal substitution is to make atonement for the sins of the elect. The main purpose is not illustrative. It's not like the moral influence theory, governmental theory, or declaratory theory of the atonement. Penal substitution is mainly about what it does, not what it shows. Its demonstrative value is a beneficial side-effect.
ii) In addition, to say God's wrath is sufficiently demonstrated at the cross renders all historical and eschatological judgments in Scripture gratuitous.
Third, given the sort of sovereignty Piper affirms, it is hard to understand what could be glorious about God’s wrath if it is meted out for sins that were causally brought about by God.
That's not self-evident. Suppose a Latin American gov't is attempting to wipe out a drug cartel. To do that, it ambushes the cartel's roving death squads. It lures them into an exposed position, where they fire on gov't soldiers, who return fire.
In a sense, the Latin American gov't "causally brought about" that confrontation. It provoked the confrontation, through a ruse de guerre. Yet the death squads deserved to be mowed down.
The doctrine of divine wrath contains two components. The first is a sense of righteous indignation towards a wrong; the second is a just punishment brought to bear on the wrongdoer. But how does one wrong God and thereby merit his wrath by doing exactly what God determines one to do?
i) There's another potential equivocation here. Notice how Adam elides wrong into wronging God. But must one wrong God to be a wrongdoer? Must one wrong God to do wrong?
ii) Even in freewill theism, in what sense does a human wrong God? A human is in no position to harm God. So it must mean something else.
The picture we are left with is a God who frustrates himself by ordaining states of affairs that he judges to be bad. God’s anger and punishment are irrational as they are directed towards objects that do exactly what they are supposed to do.
i) To begin with, there's the danger of framing this in overly anthropomorphic terms. One needn't assume that God is literally angry or becomes angry. We could better recast this in terms of divine disapproval for evil qua evil.
ii) God can disapprove of something considered in isolation, but approve of the contribution it makes to the ultimate outcome. God can disapprove of something that's evil in its own right, but which facilitates a greater good or second-order good.
iii) This doesn't mean God frustrates himself by ordaining events he judges to be bad. To the contrary, these are his appointed means to the appointed end. There's an equivocation here:
a) These are good means in the sense that they facilitate the objective.
b) These are bad means in the sense that they are wicked in their own right.
It's not as if God's means are at cross-purposes with his ends. The means are perfectly adapted to the ends.
We need to differentiate a teleological evaluation of the means from an ethical evaluation of the means, taken in isolation.
For instance, an evil man is evil whether or not he is put in the service of a good goal. It's just that some people are put into arrangements which make them unwitting allies in a cause that's better and greater than themselves.
Adam's animosity towards Calvinism prevents him from exploring or anticipating counterarguments.
How much more irrational and stupid is God’s wrath on sinners for sins God causes them to commit?
i) To begin with, there's the question of how Adam defines causation. Take the counterfactual theory of causation:
We think of a cause as something that makes a difference, and the difference it makes must be a difference from what would have happened without it. Had it been absent, its effects — some of them, at least, and usually all — would have been absent as well.
On that definition, God causes sin whether it's Calvinism, Thomism, Molinism, classical Arminianism, or open theism.
e causally depends on c if and only if, if c were to occur e would occur; and if c were not to occur e would not occur.
Perhaps Adam would take issue with that definition. It is not, however, a Calvinistic theory of causation. It's not special pleading for a Calvinist define causation that way.
Moreover, does Adam have a better theory of causation to offer? Every philosophical theory of causation is open to criticism.
ii) Moreover, Molinism falls prey to parallel objections. Although there are infeasible worlds which God cannot instantiate, God didn't choose to instantiate our word at gunpoint. He had a free hand. He was at liberty to instantiate a different feasible world. So why is he mad at the end-result of his own actions? He initiated this chain of events. He knew what was coming.