Additionally, even if the only effect of this was to have characters join a religion because it would cause them problems if they didn't then that in itself would be an achievement given the number of characters which currently remain pagans. Plus, given the way religions spread, something like this would give realms a solid incentive to try and ensure they have one religion in their land instead of multiple coexisting ones - and if that kind of religious uniformity adds a little more cohesiveness to a realm's culture and gives them a few more excuses for war with their neighbours then that's a benefit worth having on its own considering how relatively easy it would be to implement.
