Nature of Good, Evil, and Balance in the Wheel of Time
The books ARE more about balance than good versus evil. The ancient symbol of the Aes Sedai is a Ying-Yang symbol. The books show how only cooperation is the key to fighting the last Battle. When one side is out of Balance we get the decline of civilization as seen during the 3rd age.
During the last battle Rand was shown what would happen if he "defeated" the dark one and it was terrifying. The only thing he could do was seal him away again.
The Pattern itself is d
I think the reasoning in the books is that if the Dark One ceases to exist, evil ceases to exist, which means humans no longer get to choose to do good. They do good because they don't have any other choice. And Rand realizes that's no way to live. Freedom lies in the ability to choose to do good, even if it's hard. Take away that choice, and nobody's free. Rands realizes this at the end and that's why he decides not to end all evil.
