Interesting and complex topic, in fact, perhaps the ultimate question. I agree with the defense of free will, it is in my opinion the most wise and logical answer to the problem of evil.
As for the origin of evil, to attribute it to simple ignorance is to simplify the problem; evil has various causes that depend on each individual and his circumstances.
There is evil by ignorance, the explanation is simple, the person who does the evil does not know the consequences of it and therefore, acts in that way damaging his neighbor and even himself.
There is evil by stupidity, people do evil knowing its consequences and yet doing it results in prejudice to themselves and their surroundings.
And there is evil for evil's sake. I believe that every human being is capable of the best and the worst, each one has the seed of an angel and a demon in his soul that germinates according to his will, there are people who decide to do evil knowing very well the consequences of their actions and assuming them, they are people who decide to destroy the good methodically, they hate the world and the only reason of their existence is to destroy good things.
In other words, it is always a matter of choice, free will allows us to be good or evil, there is no goodness without the capacity to do evil and therefore, we all have to decide which way to go.
Moreover, if you think about it, if we were made in the image and likeness of God, God himself is capable of evil but decides NOT to practice it, so we have to decide which way to go and we CREATE evil with our actions.