Correct me if I'm wrong, but free-will theodicies are those derived from the idea that God must allow moral evil as a potential effect of free will.
A theodicy is a justification for a good God in a sinful world. What you're referring to is a free will defense, which is the attempt to logically support God's existence in relation to sin and evil. More specifically, what you're referring to is Alvin Plantinga's free will defense, which again, differs from a normal theodicy. Keep in mind this is just but one free will defense in the light of more. While I'd agree with the general concept, the idea of free will Plantinga advocates is indeed a libertarian idea, which I find to be false.
Secondly, if God disallowed moral evil, then somehow free will would not exist (keep in mind that the model of volition in play, here, is the libertarian--metaphysical, not political--kind).
Yes, free will would not exist if there was no potential for evil. Though libertarian free will I think is false for a few reasons. One concisely is that under an omniscient God that has foreknowledge of all human/natural affairs, causal and logical determinism are both true, which render libertarianism false.
But why couldn't God make us able to
(A) choose between what is neutral, what is neutral but "different," what is obligated, and what is supererogatory,
Perhaps man is capable of neutrality. Adam and Eve would at some point have had been just sitting there not doing much of anything, which I would see as sort of neutral.
What exactly is neutral but different? That is unclear to me. And God did make us able to choose between what is obligated. He prohibited eating the fruit, gave us the ten commandments. We can choose not to follow what is obligated, too. I would also have to ask what you consider a "supererogatory" act would constitute as?
(B) choose between what is neutral, what is obligated, and what is supererogatory?
Again, perhaps we did do neutral things like just sitting around. We can do or not do obligated things. I still don't know what we would consider supererogatory acts.
I'm a Christian, but with Gnostic tendencies, so I believe that one of the Persons of the Trinity is a sinner, and His sin was precisely that He created humanity as capable of sin when He plainly might have made us impeccable. However, this is a rather private opinion of mine; otherwise, it seems clear to me that God, defined as a morally perfect person, does not exist, because if He did exist and was perfect, He never would have needed to create humanity as capable of sinning.
To this I would have to say one thing: What God creates is not of God Himself, but from God. That is, creation cannot be God, especially by way of being "created." What has the same nature of God is God, and as the Son has that same nature He is God. The only thing impeccable is the Son incarnated, since it is technically uncreated as it is God. Logically then the creation cannot be the same. To expect creation to be anything but is simply unreasonable.
Also, if one person of the Trinity sinned, that would disrupt the same nature that is suppose to be inherit in all three and that which would make the other two persons not sin. So, it would not be a Trinity at that point as the one who sinned would have a different nature than the other two. At that point there is either no Trinity, or you're wrong as none would have sinned.