Ok, the spoiler tag either isn't working or I am just doing it wrong. I'm guessing it is the latter, but I have no idea what I could be doing to screw it up.
In the other films though, what evidence is there that a light side exists? To me it seems more likely that the force is naturally evil and jedi have to very disciplined in order to avoid being totally corrupted by it. Other than the Jedi saying that a light side exists, what is the evidence for it? It seems like a baseless assertion to me.