The problem here is that religions are way too cooperative / modern.
In the middle ages, you generally bashed in the heads of people with a different religion. Sometimes (e.g. Jews) you allowed them a couple years inbetween bashings so they could breed a little (wouldn't want to run out of heads to bash, would we?), but there was almost always bashing involved.
It's ok to have some cooperation, sometimes - we don't strictly simulate medieval Europe, only a "medieval-europe-like" world - but if your religion doesn't consider the majority of the other faiths as evil, you're doing something wrong.
And how likely is it that you'd go through some administrative trickery for the benefit of something you consider evil?
