I’ve defended the Free Will Defense (FWD) against some bad objections, and there are lots of them: the argument is among the most frequently misunderstood, even among people who worry about this sort of thing. But I think there is a decisive objection to the argument, and that Mackie was on to it already in ‘Evil and Omnipotence’.
. . . there was open to [God] the obviously better possibility of making beings who would act freely but always go right. Clearly his failure to avail himself of this possibility is inconsistent with his being omnipotent and wholly good (my emphasis).
Plantinga’s FWD aims to show that, possibly, God cannot eliminate all evil: possibly, every creatable being is transworld depraved, so, possibly, no matter which world God actualizes (except of course for a world including no sentient, rational, free beings) there will be some evil (someone will do something wrong).
But Mackie’s contention, and it’s a reasonable one, is not actually addressed by FWD. Mackie makes the inconsistency claim above: God is not compossible with evil. His claim is in (C).
C. Necessarily, an omnipotent and wholly good being actualizes a world that includes free beings and no evil.
If (C) is true, as Mackie contends, then it follows from the nature of God that he actualizes worlds that include no evil. The fact that we can imagine a world in which everyone is transworld depraved does not show that (C) is false, since most of the worlds God would have to actualize, under the assumption that everyone is transworld depraved, are not compossible with God. If there are such worlds, it shows at most that there are no omnipotent and wholly good beings. Let the morally and naturally perfect worlds (the worlds including no moral or natural evil) be w0 – w1000. If (C) is a necessary truth, then there are no possible worlds other than w0 – w1000, since (C) is false in every other world. So, even if there are genuinely possible worlds that fit Plantinga’s description for the Free Will Defense, it does nothing to show that (C) is false. If there is even a single morally and naturally perfect world w’–and of course Plantinga believes there are such worlds–that’s all Mackie needs. If (C) is true in w’, it is true in every world. Therefore God can create a world with free beings and no evil.
We can probably put the point more simply. Mackie’s claim, essentially, is that [libertarianism + significant freedom] (LSF) are not compossible with a perfect being. That’s what (C) tells us: namely, that God exists only if, necessarily, libertarianism is false. LSF entails that there are worlds that God cannot actualize. LSF entails (—-it’s important that you need nothing more, you need no assumptions about depravity, no assumptions about counterfactuals of creaturely freedom, no other controversial modal assumptions, full stop) that there’s a possible world in which God coexists with evil. Proof: Let w be a world with a libertarian free agent S facing a morally significant choice, A or ~A, where PA and F~A (A is permissible, ~A is forbidden). It follows that there is a world w’ in which S goes wrong (does ~A) and God exists. Mackie’s claim in (C) therefore denies that LSF is possibly true. FWD, recall, just assumes without argument that LSF is true.