These "utopia" towns never work.
I suppose a "Catholic-only" town means only the early town magisterium is capable of handing down the rules and you don't question it. This as opposed to a "Protestant-only" town where someone makes the rules and everyone questions it. :O)
Touche!
I wonder why.
The Amish seem to be doing fine. The important thing is a very high birthrate and retainment rate.