I like how everybody assumes Griffith accepting the God Hand's offer makes him evil, but why? Because they associate with demons? A logical conclusion, but we haven't yet been given evidence that being a demon automatically makes the being's actions evil. Is it because he is knowingly sacrificing the Band of the Hawk to achieve power? How is that truly any different from everything he's done so far? He was sacrificing the band to achieve power then, too. That's how war is. A person in authority or seeking authority sacrifices their military might to keep or gain power. The only real difference here is how they're being sacrificed.
One could argue the biggest problem is he's consulting with demons for power and maybe even becoming a demon himself, but this isn't a fact that necessarily needs to be problematic either.
And when it's considered he's achieving essentially godhood for the same sacrifice that when done through conventional war could have only at best granted him kingship (if even that), the sacrifice seems comparably small.
I'm not saying I agree with his decision... but from a purely logical standpoint, I can't say I disagree with it either.
It's really quite interesting stuff and this series is brilliant to portray it in such a neutral way. The most concerning issue I have as a reader with less concern about the logic of such a decision and an emotional attachment to the characters is... who's going to survive this? ._.