1) God has divine-foreknowledge of the actions of free creatures. In other words, God knows what an agent with free will ultimately chooses before that agent even actually exists. God knows if I will freely rob the bank or refrain from do so, for example. (Justification: God's omniscience).
2) Mackie's world is possible. Mackie's world is a possible world where all free agents choose to do the morally good action with every choice. In other words, no one does anything evil, so evil does not exist. (Justification: prima facie true. Though it seems improbable and odd, it is logically conceivable, so it is, therefore, logically possible. There is no reason to believe such a world is not possible.)
3) God can actualize Mackie's world. (Justification: Premise 1, God's omnipotence and omniscience. God is aware of Mackie's world and create said world, as God can create all logically possible worlds).
4) Therefore, the free will defense does not stand, as the existence of free will does not necessitate evil existing. God could have created a possible world with both free will and no evil.
Personally, I reject premise 3. The reason being that it would seem to me that God, being omniscient and with His alleged foreknowledge would not know the world "as it could be" but rather "as it would be" This is not to say God could not know what would happen if things were different, but given the variable of free agency, God would not prevent it. But even given that He does know what all free agents would do in given circumstances, to suggest God "stacked the deck" as it were, even if in our favor, would completely defeat the purpose of free will.
For example, let us say you are an avid ice-cream lover. I make a cake I would like you to eat. But, given the fact that you like ice cream over cake, I know you will choose to eat the ice cream and not my cake. In response to this, I hide the ice cream such that you won't find it, so you will eat my cake for dessert instead of ice cream. Now, while you may certainly have been free to have ice cream, by "stacking the deck" I have manipulated your free choice as to what you would eat for dessert.
Of course, trying to think of a time before God created time/space is a misnomer in and of itself. But even if we use the idea of God actualizing "Mackie's World," there is no justification to believe that such a world even was possible to exist. In Christianity specifically, God created Adam, a perfect being, with free will, who chose to rebel against God. Given these circumstances, we must recognize that
at some point, free agents, even when perfect, rebel against God. And, as noted above, "actualizing Mackie's world" is just another way of saying "God could manipulate our free choices"
There also seems to be an error in suggesting this logic based on possible worlds. When philosophers speak about possible worlds, they are referring to a world that is much like our own in which we can conceive proposition P is true. When dealing with modal logic, we use these "possible worlds" to determine how likely proposition P is true, based on how similarly the possible world in which P is true is like our own. Needless to say, it is a far cry to suggest that anything even remotely similar to Mackie's world does not exist, and such conjecture is, quite frankly, fruitless.
Finally, I wish to share that any problem of evil, regardless of whether inductive or deductive in nature, does not hold any water against Christian theism:
Part 1: The Limited Knowledge Defense (LKD) in Refutation of all Deductive Arguments from Evil:
1) If some deductive argument from evil is sound, then there is a logical incompatibility between the divine attributes of omnipotence, omniscience, and omnibenevolence and the existence of some evil state of affairs.
2) It is not the case that there is a logical incompatibility between the divine attributes of omnipotence, omniscience, and omnibenevolence and the existence of any evil state of affairs. [Limits of human knowledge must be admitted in that there logically possibly could be a morally exonerating reason for God’s non-prevention of even horrendous evils even if we do not know what that reason is, and this is true even if we have no viable hypothesis as to what it could possibly be. In order to prove this premise, one simply has to recognize that it is coherent to suppose that there could be limits to human knowledge on this topic. Provided there is possibly an unknown morally exonerating reason for God’s non-prevention of evil, there is no logical contradiction between the divine attributes and the existence of evil of any form.]
3) It is not the case that any deductive argument from evil is sound. [From 1 and 2 modus tollens]
Part 2: The Expectations Defense (ED) in Refutation of all Inductive Arguments from Evil:
1) If some form of an inductive argument from evil can provide evidence against the existence of the God of Christian theism, then one should not expect evil (of whatever form referenced by the particular argument in question) to exist if the God of Christian theism exists. [This expectation of the improbability of the coexistence of the God of Christian theism with a given kind of evil is the only possible basis for any inductive judgment that the reality of a particular type of evil makes the existence of the Christian God improbable.]
2) One should expect there to be evils (of every kind to be potentially referenced by any inductive argument from evil) if the God of Christian theism exists. [If it is the case that the God of Christian theism exists, then at least certain aspects of the Bible are generally historically accurate. In these parts of the Bible, there are evils of all types corresponding to a realistic description of the human condition concerning the experience of moral evil, suffering, and death. Furthermore the existence of these evils is explicitly guaranteed up until the return of Christ at the end of the world.]
3) No inductive argument from evil can provide evidence against the existence of the God of Christian theism. [from 1 and 2 modus tollens]
http://newapologetics.com/the-tractatus