I'm a plus one for the "idiot with a misguided and overly strong sense of justice ruins everything" camp - that sort of person could totally go to the "poor nation without a saviour" and either be manipulated into doing bad shit (eg: they said this tribe/country/race was evil and doing bad things so I killed em), or just go bad cause of the old power corrupts thing.
Or he could find out Tsukina isn't "doing her job as a saviour" by his own warped definition of justice and shit, even though the God just said she is meant to be a last resort and did the job perfectly, and go irrational rival against her. Mentioning that other nation is a hell of a flag, though getting him over there would seem pretty forced. Maybe they just invade and he blames her for "not doing her job" rather than going to their side? That's be less shitty than him going to fight for them directly IMO.
