Coming in waaaay later, but, I think that's the case. Nightingale probably has the talent of brainwashing anyone she heals, and you can see that Seiya had tear streaks running down his face.So Nightingale probably brainwashed Seiya...?
What are sins and what is holy? You need to decide what normal is first to tell that. But who decides that? What did we give someone the right to decide it?