Sephiroth literally did nothing wrong. Replay FF7. Find one thing Sephiroth did wrong.
What make FF7 great is how morally grey the plot is. You have the protagonists, who are trying to overthrow an evil corporation. They’re definitely in the right here. But then you have Sephiroth, who is just trying to absorb the planet’s life force to become a God. And he’s definitely in the right here too.