Chesterton, SJ
I would like to add, if I may, that your professor is right – free will only implies the existence of evil, it does not actualize it.
But, here’s the catch, free will absolutely means that a choice is present. If there were nothing to choose from, free will would be unnecessary. And I think it’s reasonable (and I think your professor would agree) to say that no one ever chooses evil over good. Everyone makes a choice which favors certain goods and pleasures, not evil and pain. (Even sadists and masochists choose pain because they mistakenly perceive it as a good!)
So there is a choice present by the very fact we have free will, and we only choose between known goods. God is the ultimate, infinite Good; anything and everything that is not God, is less good than He. Now, if a choice must be made, and we only choose between goods, and if one of those goods is God, any other option must be a lesser good.
N.B. To say a thing is “less good” than another is not to say it is “evil.” The lesser does not possess some good which the greater does. Evil is a lack of a due, or necessary, good on the natural or supernatural scale. But because there are greater and lesser goods, there exists a hierarchy among them.
Now let’s look at the choice again. Adam must choose between the Greatest Good and a lesser good. If he chooses God, he has done well: he has preserved in his will the hierarchy of goods and placed God properly at the top. But, should Adam choose a lesser good, say himself (because Adam is a lesser good than God), he subverts this order because God should be first in all things. This due order lacking in the second option, Adam makes an evil choice and commits an evil act, if he chooses it.
And that is exactly what happened, and continues to happen.
God love you,
sandomenico