Except that in BM, you have a ton of religions bordering each other everywhere. So since "border regions" mixed faiths a lot (relatively) in the real world, and that almost all realms in BM share a border with a realm of another faith, it's hardly surprising that people are so often soft on the issue. Other than Sanguis Astroism, I don't think any one religion has ever gained a significant contiguous spread so that any realm would be surrounded by nothing but fellow faithful.
Hemaism maybe? Eretzism? Verdis Elementum?
SA is, though, the only clear-cut example of a religious hegemony.
