First of all; the reasons we already know is meaningless since the start for Idatens(the seal is bugged)
All Idatens have been doing since the start of this series is defending themselves from demons.
1. Rin can already be pacified because she doesn't really gaf in the end, especially since we...
1. They were literally letting humans create demons for years at this point.
And it’s not like the Idaten has problem with demons, specifically at least, we’ve already seen their reasoning and that’s because demons used to just be rampaging monsters.
The reason why Idaten intervened is because...
Is this story kinda dumb? Getting edgy for no reason. Miku plan of getting demons everywhere => wins? kinda doesn't matter because Idaten doesn't really care in general.
So the only problem left is Gil, but if Miku started doing this peace thing 27 years back it's not like Gil would object...