Don't blame God for evil, because he only gave you the ability to choose to do right or do wrong. That is the freewill defense in a single bleat. Of course, there are many obvious objections that arise to this approach. The first might be to point out that choice without prior knowledge is merely shooting in the dark. He can sit in judgment of our blindfold marksmanship, but how can he blame us overly much for missing the target when he himself tied the blindfold. Anyway, who would say that it was morally responsible to hand a blindfolded man a loaded gun, spin him until dizzy, and set him loose for a game of Russian Roulette against the world?
Clearly more than mere choice is needed to determine morality. He must also furnish, along with choice, a level of light necessary to see the choices clearly. To the extent that this light appears to some and not to others we can say that some are fortunate and others are not, but is it really fair to consign to flames those whose only sin was to be born with eyes too weak to do day labor as well as others?
Likewise, nobody would fault a person for being born slow-witted, nor can we credit a person with any special moral character for being born a genius. In common parlance we say these intellectual faculties are “God-given”. Furthermore, it should be obvious to all but the most stubborn, that a genius may have an easier time making certain good choices, compared to a slow-witted person, because choice involves thinking, and the genius is, by definition, more adept at some forms of thinking. Even if we take the counter-intuitive Christian view that a slow-witted or ignorant person may sometimes have an easier time of making choices, since such persons don't tend to over-complicate things, we can simply reverse the argument and say that now, slow people end up with an occasional undeserved advantage, compared to others. In either case though, we can hardly sit in judgment of the moral character of these individuals when it comes down to biological qualities of their brains, just as we do not "blame" a person for his or her skin color, sex, etc.
By the way, it is interesting that many religious people go to great pains to insist that homosexuality is “a choice”, yet clearly nobody would say that we choose to be born a man or a woman. By being born a man we tend to have a natural attraction to women. The alternative is to say that we choose it at random, which would mean that it's a fifty-fifty deal, which doesn't match reality. Clearly, if males are naturally predisposed to like women, and women are naturally disposed to like men then we can imagine that wires get crossed and some men end up being naturally disposed to like men. Futhermore, you will note that, the fact that there is choice in the equation still doesn't entirely address the situation. Sure, there is an element of choice, but the choice is a biased one, because, without an inborn, hormone-based biological sex drive, we might not have ever been tempted to philander or “transgress nature”. Therefore, at best we can say that choice is part of the equation in terms of sexual “immorality” and that the other part is not choice-based.
Thus, so far, we have established that moral decisions are based not just upon free will, but also starting knowledge, inborn intellect, and hormonal levels. If we cannot blame God for these factors then whom should we fault? We might say it is “nature”, assuming that god surrenders his prerogatives to its randomness, but this still does not make human free will 100% culpable for the amount of evil in the world.
This says nothing of the more traditional objections, such as natural disasters, which likewise undermine the doctrinaire view that 100% of evil can be attributed to free will. Indeed if even a small percentage of evil can be attributed to factors other than free will then this still creates a problem for the defense. Something else must account for these kinds of problems. While we might attribute natural disasters to mere misfortune, rather than evil, we cannot say that evil created by people who are ignorant or slow-minded is merely misfortune. Nor is pain alone the measure of these evils and misfortunes. An ignorant person may not experience any pain due to some poor choices, and others may not necessarily feel pain from their choices either, but the choice can nonetheless be the wrong one.
Still don't believe me? What about Saint Matthew who famously observed that, "The spirit is willing, but the flesh is weak"? (Mt 26:41). Despite our best efforts and desires to make good choices, our "weak flesh" rebels. This apparently lead Saint Paul to theorize that, "if I do what I do not want to do, it is no longer I who do it, but it is sin living in me that does it". (Ro 7:20) This is hardly a vote of confidence for free will, because it says that your actual will is thwarted by naughty tendancies within the body itself, which overwhelm the will. Therefore even people who want to be good, like the saints say that they are unable to do good, despite their desires to behave morally. This makes a naive invocation of "free will" as an explanation for the existence of evil completely untenable.