I would rather see Cicily butchering that priest. I know the diplomatic implications, but can anyone really stop him if he wanted? Also, I understand that there would be some complications but with the popularity and support that these guys receive and the unpopularity of that archbishop, they could very well take care of those complications and even get the good guys image. Or could even cover up everything easily, given Shin unreasonable power. Not enough evidences, making trouble to the ultimate magicians(plus kingdom) wouldn't be wise. I believe(jk, I don't believe, I hope) the holy nation knows better(even though they absolutely missed in who to send as representative). And that guy could have been a thorn in someone's else hand. So why not show some gratitude by shutting up.
Well, of course, most can only happen if that priest was already a bastard. Anyways, no one needs a huge argument to justify murdering that guy. People already killed for less.