Originally Posted by Skyblade
Actually, the paradox idea has quite a bit going for it. For a moment, compare it to the Terminator movies. Anyone who has seen through to Terminator 3 knows that no matter what the good guys do, Judgement Day still happens, and the machines still rise to power. It is said that Judgement Day is "inevitible". Why is that? Is it because of fate? Not at all. Remember, the time machine was created by the machines, not by humans. If you defeated the machines, where would the time machine come from? Though not as obvious of a parrallel, if you defeated Junction Machine Ellone, and Ultimecia didn't come through to the past, how would Squall and company have known they needed to destroy JME? They only know to destroy it because of Ulti's interference with the past. If the stop Ulti's interference, they also eliminate the reason they stopped here interference, which means they wouldn't have stopped her, but then... It's a paradox. Of course, if you believe in a set timeline and fate, it doesn't work. But, if you hold different beliefs, then a paradox could indeed be the cause.
I prefer my previous explanation (the one paradox already in the game is enough for me, no need to add another one), but this argument is definitely valid.