Yeah it was the Infinity arc where things started going to Hell. Things were sane during Acid Tokyo but after the fandom fell apart.

I'm really not sure why they're convinced that Nihon is next. I heard plenty of people say that Tomoyo can use magic to heal Kurogane but I don't know if that's the only reason why they think it'll happen.

I agree with you, there's no real conflict going on there so there's no reason to go now. Kurogane has already said he wants to get revenge so it's not like there's this big dilemma where they'd have to convince him to continue with the journey.