With the way the story's going, the whole "Darkness isn't evil" thing seems to have been shot down by the "7 Lights = good guys, 13 Darknesses = bad guys" deal. It looks like MX is only proving Eraqus right about Darkness more and more.
Uh... No it doesn't, lol. It all goes down to how Master Xehanort is utilizing every means possible to get a hold of various incarnations of himself to orchestrate another Keyblade War, obtain the Xblade, Kingdom Hearts and bring an eternal equilibrium between light and dark.
In summation;
It's an anti-hero getting more and more violent, not that darkness is becoming evil. =/
Hopefully we'll get a Light-based enemy to counteract that.
We've had enemies that represent the Realm of Darkness (Heartless), Realm of the In-Between (Nobodies), Realm of Sleep (Dream Eaters/Spirits/Nightmares) and no realm at all (Unversed). The last to represent any realm are creatures of the Realm of Light. Maybe they were sealed somewhere and Xehanort unleashed them to mess with the Princesses' worlds to get a reaction from the heroes?
I mean, I don't mind the plot, they have set it up very well with little hints here and there that you pick up after knowing what's actually happening. But my issue is with Xehanort's reasoning. I find it very peculiar that Xehanort knows that 7 lights and 13 darknesses need to clash and he is very confident that 1 of the lights is on his side. Xehanort wants the lights to clash with the darknesses, so why would he want lights on his side? That would just screw with the numbers and his plan. I mean, I suppose you could say that Lea and Kairi could fill in for Sora and Terra as lights, but Xehanort obviously didn't know about them, hence Lea's interference with Sora's Nortification. Meh. I don't know. Something just doesn't add up there.
Uh... The Seven Lights are presumed to be Master Aqua, Master Riku, Sora, Kairi, Lea, Ventus, and Master Mickey. Both Riku and Sora were considered to occupy the 13th chair on the Xehanorganization, both are now irrelevant. Riku because he built a strong resistance against darkness and Sora because, after all the trouble they went to force him in, they decided to quit. There is no one in the Light side that Master Xehanort wants, on the contrary, he
wanted. And if you're thinking Ven so he can get the Xblade, which should answer your following question, then this is the case;
There are TWO scenarios by in getting the Xblade:
+ A heart of pure light and another of pure darkness unite.
+ A clash between keyblade wielders of light and dark happens (Keyblade War).
Xehanort is doing all these to recreate a Keyblade War so he can get the Xblade, summon KH and become an all powerful being to shape the world to his ideals (a balance between light and dark). He's like an anti-hero becoming a heroic dictator.
That's the Xehanort Saga in a nutshell;
An anti-hero that wants to become a God, play A HELL LOT OF GAMES to progress and finalize the plot.
That's also the series in a nutshell;
Play these ridiculously-fantastic games (ridiculous-plot, fantastic-gameplay) to progress and finalize the series' story by playing various games available on various consoles! :]