The thing about FFIX's villains is that none of them is really purely evil, as they all (SPOILER)have some sort of redemption or heel-to-face turn during the game. This applies to Beatrix, Brahne, Garland and Kuja. That's why I think the game needed Necron as the final boss. He probably can't be called evil, either, as he's more like a force of nature rather than a person, but this way, you get to fight a foe that can't be redeemed. It's also symbolic for the game's main message, which is about finding yourself and your purpose in life, and the final battle has your party members fighting a force of nature that wants to end all life (i.e. death). Plus a reference to FFI, FFIII, FFIV and FFV. Anyway, Garland may have a noble cause, to restore a lost civilization, but he uses questionable methods for it, such as robbing Genomes of their soul and free will, and attacking Gaia so that the planet could be assimilated. Eventually, though, he returns to help Zidane and others to stop Kuja from ending all life.