Matt Slick offers some reasons why evil exists. Here is his second possibility:
Second, God may be letting evil run its course in order to prove that evil is malignant and that suffering, which is the unfortunate product of evil, is further proof that anything contrary to God’s will is bad, harmful, painful, and leads to death.
Note the twisted logic here. God is attempting to prove something to creatures he could have just predestined the believe that same thing without all the fanfare. If God predestines everything, evil existing to prove a point or illustrate a concept becomes meaningless. After all, it would have been easier and less evil just to predestine that everyone just understand the concept of evil, rather than predestining evil to prove to people who are totally depraved something they could never believe unless predestined to do so. The sheer irrationality embedded in Slick’s number 2 possibility is countless.