So, imagine... Yen Sid, Mickey and Eraqus are in fact the bad guys who are mind controlling everyone to keep them subdued and under the control of the "Light". Xehanort, filled with curiosity, found stuff about this in his early years, and decided to oppose their tyranic rule with all his might, and instead of being the bad guy, he's good... just he can't go about telling everyone the truth, for none would believe him, since they are partly being controlled...
mundf*ck, huh? XD don't worry, it's just that I lack proper sleep and I've been playing a bit too much Assassin's creed, and as I cooked my dinner, I pondered on what would happen if Disney acquired the Ubisoft franchise, and suddenly everything became all too similar XD except that for this theory to happen, KH would need to be a universe that went full Templar, with most, if not all Assassins killed in the Keyblade War lol Think of it if you've played both... they're eerily similar... or maybe it's just my half, self drugged brain XD
You can even guess that, since masses create collective thought and rebellion in time, the ones who "fight for the Light" (Templars, yeeeh) would have divided the One World into many, to keep people sepparated and in small, simple places that would not allow the environment to develop a proper revolution and would be easy to deal with in case they found anything out. When you come to think of that phrase "the people in these worlds must never know about the others" (BBS, I think), it turns daaark and ominous, and totally Templar word XD
I'm not familiar with Assassin's Creed IV yet (they delayed the shipping in Mexico until friday T__T), but for what little I've seen on Youtube, the mentions they make of the Observatory somehow reminded me of Yen Sid's place. Still, I haven't seen beyond Havana in these playthroughs, so I am most probably wrong about that relation xD
On the AC part, I sort of find fitting the motto of the Assassin's for the true Organization XIII. Applied to Kingdom hearts, saying that "Nothing is true, everything is permitted", well... the various Xehanorts are dead set in their belief that that of the light is a tyranic rule that forces people into obedience, and that of the worlds is not a functional society, hence, it needs a "new rule", one that balances everything and (probably) grants everyone freedom. Also, they pretty much live with every consequence of their actions, which is the "everything is permitted" part.
On a minor line, the oath made in the ascension ceremony is "we work in the dark to serve the light". That would be kind of forced, but I would not doubt that "light" in this particular case would not mean "the Light", but "enlightenment", or the forging of a path to show the truth to others. You can't say that being an Assassin is either a pretty, safe or legal work, yet thinking of it, some have to sacrifice themselves for a greater good, and they usually choose the path knowing that they will not be well seen or accepted by those who cannot see "beyond" <.<;
Another thing is that as soon as I saw Haytham in AC3 I disliked him, and he turned to be one of the bad guys... then I remembered that around 70-80% of the times, the guys I like tend to be good in their own way, and the ones I dislike end up being vile deceivers >.> *le-deep sigh* anyways, I should be writting an essay for school, and since I'll probably have AC4 this friday, I won't work on that this weekend, so better get to that xD
Last: If you read this far, I hope I gave you some material to think about, and well, good luck with the nightmares I might have caused lol