Originally Posted by KaiserDragon
Spoilers...
In Kefka's case I think that the principle "absolute power corrupts absolutely" applies. He started as a loyal servant of the emperor, even if his ways were inhuman, unlike that of General Leo. He poisoned the water because he wanted to get rid of the people who "gave rise to the returners". He burns figaro castle because he wanted to recover Terra, a woman that belonged to the empire, which Edgar and Locke hid there. But later he starts to become obsessed with the power of Magicite and starts to claim their power for himself and becomes obsessed with it to such an extent that he ends up killing anything that gets on his way, including the very emperor who he served at first.
Having an absolute and destructive power now, all that he can do is use it to destroy the world around him. As the dialogue before the last battle shows, he felt that human life was meaningless, that it was a waste of time because people were going to die anyway so he felt that a "monument of non-existence" was better. This reminds me of Seymour's idea of ridding Spira of it's sorrow by destroying it.
