Completely agree, K. That's why I said I think it constitutes a good argument for God's existence. Really, the only way out of it is to embrace nominalism, which is such an amazingly
stupid position it's one of the few things that still surprise me when (educated) people claim to hold it.
As to the argument I put forward about rejecting Platonism, there are, sadly, theists who have expressly argued that not only are universals
not contingent, but that, in fact, God is contingent
on them. Alvin Plantinga is the most important name that immediately springs to mind saying this. To quote him directly,
- If God were distinct from such properties as wisdom, goodness and power but nonetheless had these properties, then . . . he would be dependent on them in a dual way. First, if, as Aquinas thinks, these properties are essential to him, then it is not possible that he should have existed and they not be ‘in’ him. But if they had not existed, they could not have been in him. Therefore he would not have existed if they had not. . . . The point is that he would be dependent upon something else for his existence, and dependent in a way outside his control and beyond his power to alter; this runs counter to his aseity.
Secondly, under the envisaged conditions God would be dependent upon these properties for his character. He is, for example, wise. But then if there had been no such thing as wisdom, he would not have been wise. He is thus dependent upon these properties for his being and the way he is . . . and there is nothing he can do to change or overcome it. . . . And this doesn’t fit with his existence a se. (Alvin Plantinga, Does God Have a Nature? (Milwaukee: Marquette University Press, 1980), 32-33)
And on the very next page, he says . . .
- Now I think the intuition—call it the sovereignty-aseity intuition—underlying the doctrine of divine simplicity must be taken with real seriousness. Suppose God has essentially the property of being omnipotent and suppose that property is an object distinct from him, is uncreated by him and exists necessarily. Then in some sense he does depend on that property. For in the first place he could not have existed if it had not; its existence is a necessary condition for his existence. And secondly he couldn’t have the character he does have, couldn’t be the way he is, if omnipotence didn’t exist or weren’t the way it is.
Anyway, that whole book is dedicated to the notion that we ought to reject this sovereignty-aseity intuition. God, for Plantinga, really is contingent on the universals in question. That is, he just regects God's aseity. I don't see how that works, as to your point, that means that the universals are not contingent on a mind, plus the additional argument I put forward. Augustine, though, for all his mistakes, at least saw this clearly, and made the "eternality" of the universals the very thoughts of God, which is obviously much closer to the truth.
In any case, your point, as far as I see it (?) is really beautiful and easily extended: if nominalism is true, knowledge is impossible; but knowledge is possible, so nominalism is false; so universals are real; but universals necessarily presuppose a mind; so a mind exists upon which universals are contingent; such a mind can only be described as God; therefore, God exists.
edit:
Moreland and Craig, by the way, were in agreement with Plantinga, at least at one point. These difficulties are openly admitted and no solution is offered in their
Philosophical Foundations (504-507, according to my notes, but I don't have the text in front of me to confirm that).