Morriston on Sourcehood Accounts of Libertarianism and the Free Will Defense

Suppose one replies to the criticism of Plantinga's free will defense we've been discussing as follows: 

Since God is morally perfect essentially, he is unable to sin. However, he's still free and morally responsible. For even though he's unable to do other than what is good, he is the ultimate source of his actions. That is, he acts on his own reasons, and nothing external to God determines his actions. By contrast, if God created persons with a morally perfect nature, they could not be free or responsible. For such beings would not be the ultimate source of their actions. Rather, God would be the ultimate source, as he would be an external cause of their nature, which in turn would ensure that their actions are always good. The only way for God to create free creatures, then, is to create them with the ability to choose between good and evil. Therefore, while the freedom of created beings requires the ability to do evil, God's freedom does not. 

Let's call this The Sourcehood Response, since it appeals to a sourcehood account (as opposed to an alternative possibilities account) of libertarianism in response to the criticism we've been discussing. In "What Is So Good About Moral Freedom?" (The Philosophical Quarterly 50:3 (2000), pp. 343-358. ), Wes Morriston argues that the Sourcehood Response is unsuccessful. To see why, consider two finite persons, Alpha and Beta[1]. Alpha and Beta are both morally perfect, and thus unable to do what is morally wrong. They differ, however, in their origins: while Alpha was made to be morally perfect by external causes (e.g., God, or heredity and environment), Beta was not. Rather, Beta just popped into existence.

Here's the punchline: if the account of freedom and responsibility in play in The Sourcehood Response is correct, then we should say that while Beta is a free and morally responsible agent, Alpha is not. For while Alpha's nature was caused by an external source, no external source caused Beta's nature. And because of this, we should evaluate the following subjunctive conditionals differently:

1. If Alpha existed, she'd be free and morally responsible. (F)

2. If Beta existed, she'd be free and morally responsible.   (T)

But this doesn't seem right: whether their natures had an external cause doesn't seem to make a difference to the issue of whether they're free or responsible.  What matters here is that the actions of both are due to natures they did not create and for which they are not responsible. Thus, either being is free and morally responsible just in case the other one is.[2] The Sourcehood Response is therefore an unsuccessful reply to the criticism of the free will defense at issue.

Morriston anticipates a reply on behalf of the Sourcehood Response. Thus, someone might argue that the scenario depicted in Morriston's thought experiment is metaphysically impossible, on the grounds that it seems metaphysically impossible for a being to just pop into existence. In response, Morriston argues (roughly) that whether the scenario is metaphysically possible or not is irrelevant. For per impossible arguments clearly have epitemic force, and are often used for evaluating counterpossible conditionals.[3] The rejoinder is therefore unsuccessful.

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[1] Here I've slightly modifided Morriston's thought experiment, replacing his 'the alphas' and 'the betas' -- groups of beings -- with just two people.
[2] Morriston argues for the stronger point that neither Alpha nor Beta is free or responsible for their actions (as each is subject to a nature it did not create), and that since this is true of Plantinga's essentially morally perfect God, neither is he. I'm not so sure about that, as I have compatibilist leanings. 
[3] I would add that counterpossible reasoning had better be legitimate; otherwise it'd be impossible in principle to evaluate competing philosophical theses, each of which is necessarily true if true at all.