>"Would it be fair if England declared Catholics “unChristian” and banned their use if the term?"

I assume you know that happened all the time during the Reformation period with Henry the Eighth starting it, with a contrasting bit in the middle where Bloody Mary persecuted non-Catholics instead. They were bored and the internet hadn't been invented yet.

Once kings and queens weren't in charge, things got a lot more relaxed in that area.