Wow....
FFVII sure was a religious experience for you, wasn't it?
And is this a thinly veiled LT discussion, or is that just me?
First off, Aerith didn't sacrifice herself. She did not intend to die. She was murdered by surprise by Sephiroth. So saying she sacrificed herself for the planet is erroneous.
Cait Sith's "sacrifice" was a parody of death in video games. How it's built up and done all dramatically and sentimentally so that when it does happen its not nearly as gut renching because you saw it coming and thus, are able to accept it. It's totally different than how Aerith's death happened suddenly, without warning, and without her intention. Furthermore, Cait Sith came back. That's hardly a sacrifice at all. He's just a stuffed animal controlled by Reeve. That was explained in EDGE magazine and then in the interview with the creators in the 10th Anniversary Ultimania.
Aerith was not the only one who knew Cloud wasn't really himself. Tifa knew it too.
And no, the ending didn't represent the end of humanity because we see, 500 years later, that humanity still exists. We hear the laughter of children in the background.
And while FFVII has a great, enriching story full of memorable characters and themes about life, love and never giving up, its preposterous to say that it's on the level of actual literature. It can stand up to some of the contemporary stories and novels out today but equating it to works literary merit is naive and to some who appreciate classic literature, an insult. They're not in the same league and the creators never tried to put it there.
I hate to break it to you, but FFVII is a game. A fantasy RPG. It's a good one, but please. Don't build it up as if it's some type of life changing experience. This is the exact shit that gets FFVII's mocked by the rest of FF fandom and fandom at large. Keep your perspective. FFVII is hardly the pennacle of storytelling excellence. That's naive.