I look at it as a tale of two runes/runebearers. The original Flame Champion was able to remove his rune and live out his life and die. I know that this is up for debate in another thread, but every True Rune bearer is said to be cursed with immortality. I believe that Geddoe says he is trapped in the purgatory of life. Almost all of the TR bearers want to die. In the end, all of them can die. All they have to do is transfer their rune to someone else, like Ted, Neclord, Joshua, FC did. I think Luc is slightly jealous of all other TR bearers. Since his rune is fused to his soul, he can't get rid of it. Therefore, he can't die a natural death.
He also hates Harmonia for botching his creation. Since they're trying to collect all the TRs, what better way to foil their plan than to destroy one.
His vision is just self-justification for destroying millions of people. Not to say that he didn't actually see it. But he is the fool if he thinks he's being noble and saving the world from stagnant order. He's just pissed off and feeling sorry for himself.
But I love his character. I don't think any other character has the level of depth that he has.