I don't like the presence of evil for the sake of a balance between good and evil either. It's a good idea, but never done the right way. Good and evil is in everybody. That's all a matter of what you choose to act upon.
I thought of a story concept involving four powers: Day, Night, Twilight, and Dawn. Obviously, Day and Night symbolize the standard good and evil powers at play. Then what's Twilight and Dawn? Twilight is the powers of the Night acting for the Day, and Dawn is the opposite. There was no obvious line between good and evil in this story. It's supposed to illistrate that it doesn't matter what sort of powers there are, good and evil is all a matter of point of view.
Which is kind of why Sith bug me. Unless I look deeper into the creation behind the Sith of Star Wars, I just see the standard good vs. evil. But wait. Jedi trust their feelings, but they don't act on them. They can't do some things other people can, like fall in love and get married. Sith, however, act upon their feelings. If they're angry, they go on a rampage. But what if they're happy? Do they still smile and walk with a bounce in their step? Jedi have to remain calm at all times. I've never seen Jedi exchange jokes before, have you? And so we have a fine way to blur the lines of good and evil. Good means suppressing emtion so it doesn't cloud your judgement. Evil means using the Force to your own will.
I can't mention Sith and Star Wars without mentioning Anakin too. This guy is BA in episodes IV - VI, and then he gets a whole freakin' trilogy to explain his story. That's just sweet. Props to you, George Lucas.
If you want a good story, blur the lines of good and evil. What makes a person good? What makes them evil? Is it accepting only the 'right way' to do things? But isn't a good person supposed to consider all options before making a sound decision? That involves tainting your hands sometimes, doesn't it? But if a decision is made for the right reasons, surely that must mean their hands won't be tainted. But isn't that what the standard bad guy is doing? They don't believe they're wrong. Oh, the possibilities with this kind of thinking!
If ever you want to write a good story, think of something where good and evil are blurred. If you have a story on one side, you must have a story on the other. Let the reader figure out all that goes on.
There are always two sides to a conflict. There's Side A and Side B. The third side, Side C, is a combination of both sides to discern the Truth, which is always somewhere in the middle. That is the kind of story I want to read whenever I sit down. I don't want "good vs evil", I want "are they really doing the right thing?" It's this way of thinking that makes a really good story.