Sure, some smaller churches will literally forbid you, and cast you out from other parishioners. But in the grand scale of things...
While other religions will cut your head off if you don't believe, or believe elsewhere, or believe in another religion. Being "forced" to marry elsewhere isn't so bad in comparison. Even being a cast-out and being "forced" to worship elsewhere still leaves one alive and as free as can be.
Folks have choices. They know their religions, their faith system and what the rules are of the places they CHOOSE to be members of. And like any other place in the world that has a member based system, it has it's rules.