I, for one, have discriminated people based on religion a lot, throughout time, but very discreetly. Whenever two candidates for a position were running and one was of a faith I liked and the other of one I didn't or of none, I'd secretly petition for my favored candidate, even if these were often much newer, less experience, or known to be outright reckless. And this was (at least almost) always done extremely subtly, never with any reference to religion at all, and so trends in religion come up as being spontaneous evolutions, and not as having been orchestrated in any way.
I was wondering if others did the same, and/or realized that not joining a faith can in some places be costly for one's ambitions. It's amazing how much one can silently influence results, if within the proper contexts, and so I'd expect others to do the same.
I've only done this consistently with one character, but yes, it seems like a medieval thing to do.
