What Griffith did is horrible but even if not agreeing I have empathy for him and I can understand why he decided to do it: a person like him that had everything wouldn't ha ve ever been able to accept a life without anything forever.
Anyone would have done what Griffith did, he lost his dream and was crippled beyond recovery.
The thing that makes him a great character, is his determination, he even made the world a better place
Well, I'm not saying that everyone would do what Griffith did, just that from someone like Griffith this was the most logical thing to expect. If you take an incredible ambitious and again succesfull man that put his dream in front of everything and then you take away everything, very hardly he will be able to continue to live in a such way.
Anyway people forget often that the relationship of Guts and Griffith is first of all the one of a great lost friendship than a revenge and that Guts is the only person that was able to be considered from Griffith more important than anything.
I'm pretty sure that in his final moments after the fateful duel with Guts, Griffith will realize the mistake of that day and genuinely will regret everything asking forgiveness for it to him and maybe Caska too.
PS: About making the world a better place... just expect for the people of Falconia to become the next mass sacrifice as happened in the old Midland capital
As the witch Flora stated, the karma proceeds in spiral and the History repeat itself even if with variations: the current story of Berserk appears actually to be a retelling of the old events of 1000 years ago even if with differences. In the past there was the condoitter Gaisserick that used the beserker armor,
become the imperator of his reign, then saw the destruction of it through an eclypse and then very likely was reborn as the Skull Knight against the God Hand.
Now it's happening the same but with two persons: the condoitter is Griffith that is close to becoming the king of the Midland and actually is part of the God Hand; the berserker knight is instead Guts that continue to fight against the GH even if losing his humanity (also he is going to the land of the Elves and Puck stated that SK had something elven in himself).
For these reasons seems to me pretty likely that the fate of Falconia will be the same or close to what happened to the old Midland. However about the actal reason for it, honestly I don't know...
From a side make strange to think that Griffith want again destroy his dream, from another is also true that now that he is a semi divinity, make strange to think that Griffith can still wish only to be a mere king of an human reign. He could have still other plans, maybe against the other God Hand or the same Idea of Evil (the God). Or maybe just the other members could have a secret agenda against Griffith.
so much to talk about, and i don't even think the manga was ever finished! (i only read up to the part where Guts fights the dragon in the berserker armour, so pretty far, but nothing more.)
The manga is still not ended (sigh, there are still years left...) but many interesting things happened from the "fight with the dragon ", even if overall related to Griffith. When you have time I suggest you to continue the read =)
yeah i'm reading this manga atm, It's called Vento Aureo, i don't know if you've heard of it but it's pretty darn good so far, character designs are a bit out there but hey it like it