@mattman33,
Logically, there is no good without evil, just as there cannot be day without night.
A universe without potential evil, would have no good either.
Try and play God. Write a story without an antagonist, or without a distinction between good and bad. Its just ridiculous to ask for a world of good without evil. It makes as much sense as having up without down.
Karma only half explains the issue. If all good and bad actions were the result of Karma, then how did the first bad action take place?
If the worst thing that happenned to anyone was to stub her toe, then that would make headlines as a global catastrophe, and the faithless would consider it to be evidence that God was not omnipotent.
The Aquinas quote is an excellent one to begin with. The universe is perfect because it has the freedom to result in any event. Anything less would appear kitch, and the atheists, now full of faith, would complain that the world was not intense or real enough.
A square circle = a cylinder.
Look at it from the side, it appears square.
From the top, it appears as a circle.