Every once in a while I'll realize that two or more very popular positions for theists to hold are inconsistent in some subtle way, for example divine command theory and the free will defense / theodicy. I'm going to focus on the free will defense because face it; the free will theodicy is useless. The free will defense, on the other hand, seems to be the only answer to Mackie's logical problem of evil.
According to divine command theory, the property of goodness is identical to a relation to God's essential nature. Thus, an instance of a good thing is an instance of a Godlike thing; a thing that bears a likeness to God's essential nature. And so love and justice and so on are good just in case God is loving and God is just.
Now according to the free will defense, it's possible that God permits our immorality all for the greater good of preserving human free will. Of course the type of freedom here is much stronger than mere libertarian free will, as libertarian free will only requires that there be a possible world in which either outcome is chosen (they need not involve a bad outcome, or even a morally significant outcome). What is required to make the defense work is libertarian free will plus a little more: a possibility of us freely choosing evil. I'll call this sort of free will "freedom+", as possessing it involves not just genuine free will, but freedom to participate in immoral behavior.
Notice, though, that there's no possible world in which God participates in immoral behavior; by definition he holds moral perfection as an essential quality. Furthermore divine command theory requires God to be essentially morally perfect. How could he be the arbiter of morality otherwise? Therefore, while God may make genuinely free choices, he does not have freedom+. But if God does not have freedom+ and divine command theory is the case, then freedom+ cannot be a good thing. And so given that divine command theory is true, the free will defense fails to identify a greater good that would prevent God from eliminating the evils resulting from our immoral behavior. Of course it goes the other way too; given that the free will defense is valid, freedom+ must be a good thing. But if freedom+ is a good thing then God possesses freedom+, and so God cannot be essentially morally perfect and as a result divine command theory fails.
And so what results is an interesting little argument:
1. If DCT, then X is good just in case God is essentially X
2. If FWD, then freedom+ is a good thing
3. God does not have freedom+ (because he is necessarily morally perfect)
4. If DCT, then freedom+ is not a good thing (1&3)
5. Therefore, not DCT or not FWD (2&5)