Were they a good thing in general ? Both Sephiroth and Jenova tried to destroy the planet , and it was a terrible thing to most of you . But if you look at it from a different point of view , they were actully doing a good thing . Me and my cousin having been looking at this alot . Since the planet had terrible things in it .
Sephiroth was using the planet to improve himself and bolster power to become what he thought of as a god. The planet wasn't a very good place, but really that was because of the people in charge who had made it a living hell and others weren't really doing things about it. Sephiroth was pretty well driven mad and also misled by notes of Hojo's to thinking that Jenova was a Cetra at first. Later, I'm sure he knew what the deal was but he was more concerned about the matter of just moving on and not really caring. In a way, I debate if in the end he even cared if he lived, but had a sort of honor that wouldn't just let himself kill himself. As for Jenova, it seems the way they made her out to be, was that she was kind of a big virus in a way. She didn't have much of a personality and was a devourer of people, mimicking those she had destroyed, changing forms etc to match those who had died back in the Cetra times. She had to be dealt with in the past and because she was an entity that fed on life, when the doctor who had found her discovered the fact she was clearly not an ancient one, (Dr. Gast), he fled. Sephiroth had respect for Dr. Gast, but Dr. Hojo continued experimenting etc. Jenova wasn't really doing what she was because the planet in any way mattered to her or not. Where Sephiroth had some emotional level of concern about the world, pointing out about magic dying etc, Jenova herself was simply in it all for the food because humans taste crunchy in milk. She was an alien life form that did not have a concern for anything other than that. By what I could get of the story of Advent Children as well, Sephiroth had a very strong will and presumably that will may have been enough to take over the Jenova cells and such, but not enough of one to fight the driven instincts that Jenova had that he had to feed on spirit energy, and also not enough to grant him his sanity back. Of course with all that had happened to him, that sanity would be hard to come by since there was nothing in his life he really had to care about that would prompt him to gain his -human- emotions back really. So he was lost essentially and just didn't care anymore, which is why I can imagine he was just messing with Cloud, because in the end, he expected to be defeated or else he would have actually slain Cloud. He just had no real ambition anymore and was just a lingering entity. Watching the 3 (Kadaj, Loz and Yazoo) gave a view into former pains of Sephiroth but I doubt he had any himself upon being reformed to at least 1/3rd his former power. Had he gotten all 3 of their aspects to himself, maybe there would have been more to see of a personality, but I doubt it.
