Ah, here's where I lack any links to back myself up. There was an interview with Lucas around the time that TPM came out that generally espoused this exact theory, including the part about how the Dark Side is unnatural. But I can't for the life of me track it down. SW isn't as organized as HP when it comes to creator interviews. My reasoning for that view is that while the universe may be amoral, it's not evil. Animals don't kill out of hate. And yeah, this gets sticky since I don't really think humans can be unnatural, since they are products of nature, but let's just say that the Force isn't hateful because hate doesn't produce more life. But the Force isn't big on doing stuff -- that's what the Jedi are for. So the Force doesn't actively support the Sith, it merely allows their existence, which sets up a conflict that brings the Jedi closer to the Light. At the end of RotJ, whether you take a numerical view of balance or not, there are no Sith left. That leaves the Dark Side without focus. One can argue that Light and Dark are balanced within Luke, but I think that ignores the sheer virtue of his acts at the end of the movie.