The free will defense can be viewed as an attempt to show that there some kinds of good that even an all-good, all-powerful, all-knowing God can't bring about without permitting evil. The version below is modeled (loosely) on what Alvin Plantinga says.
1. Creatures who are significantly free cannot be causally determined to do only what is right.
2. Thus, if God creates creatures who are significantly free, He cannot causally determine them to do only what is right. (from 1)
3. Thus, if God creates creatures who are significantly free, he must create creatures who are capable of moral evil. (from 2)
4. Thus, if God creates a world containing creatures who are significantly free, it will contain creatures who are capable of moral evil. (from 3)
5. If God creates a world containing creatures who are capable of moral evil, He cannot guarantee that there will not be evil in that world.
6. Thus, if God creates a world containing creatures who are significantly free, He cannot guarantee that there will not be evil in that world. (from 4 and 5)
7. A world containing creatures who are significantly free (and freely perform more morally good than evil actions) is more valuable, all else being equal, than a world containing no free creatures at all.
8. Thus, God has good reason to create a world containing creatures who are significantly free. (from 7)
9. Thus, God has good reason to create a world, which He cannot guarantee will not contain evil. (from 6 and 8)