(Nice spelling on my name, Lep

)
From the Tao Te Ching -
"What is the wise man but the fool's teacher?
And what is the fool but the wise man's student?"
Having read Gollum's essay, I would like to say that the concept of 'eternal balance' stretches farther than what you've said, in my mind.
The Buddha, after years of both extreme comfort and carefree life and then of extreme ascetism and suffering, found Nirvana by staying in a place inbetween. What always struck me about this final reaction is that he taught others to avoid extremes completely; didn't he
learn that by being extreme in the first place?
In relevant terms - extremes of good and evil have to exist if a balance inbetween them does as well. Zoroastrianism (sp?) and Catharism, to name just two, have the 'God and the Devil' concept, that good things are of God's making, and evil things the Devil's. If a religion says that 'everything was made by a neutral force', then, well, that's fine, but that leaves absolutely nothing to do. If good is fine, and evil is just good in the long term, that leaves everyone with absolutely no reason to do anything; you can just lie around all day, and it'll all turn out for the better in the end.
Thus the religions or philosophies that are really noted are the ones who do advocate some extreme lifestyle, even if they call that extreme 'balance'.
So, I look at it like this. Good and evil are just words attached to different mental indicators that we have to tell us what is destructive and what is productive; the actions that trigger these are independant of these feelings, so likewise emotions have the capacity to exist independant of what is real. That's why, I think, different people have different concepts of time; thats why we can look back on particularly painful or particularly beautiful moments as lasting an eternity.
Since by that theory, everything, including time, space, and pretty much our whole world, is in our mind, then yes, people do have the capacity to live lives in which the world is one-sided; where they see everything as good or everything as negative. But I think in plain, perception-free (so to speak) reality, negative things must occur for positives, even though we as humans may, by our own choices, subliminal or otherwise, not have to feel emotions on either side of the spectrum.
For example, 8th grade for me was probably the best year of my life; I was in a place where I was totally secure and confident - I knew my friends, knew my enemies, I pretty much had it all figured out. But when I look back on it now, in reality it was not such a good year; very tumultuous time for my family, and my relationships with some people I thought my friends were not so good as I thought they were. However, in the end, it still doesn't matter to me what actually happened; it matters that I felt that way.
So to extend on the first quote - since we're humans, and we have choices, wether or not our instincts influence them, we do have the capacity to be all 'fools' or all 'teachers', but if we do, then there is no longer a reason to be either.