OK, it could as well be it has shifted, but I do not think the roots are in the Catholic-Protestant struggle as well. The same thing can be said of the Netherlands by the way - my father (who's Catholic) was not allowed to marry or even date a Protestant girl. That phenomenon seems to have stemmed from the fact that some centuries ago, some (Protestant) provinces managed to escape from the (Catholic) Spanish rule. When after some time other Dutch provinces joined them, which were however mostly Catholic, the Catholic Dutch were long accused of being more loyal to the Pope (and the Spaniards) than to the new (Protestant) rulership. Those accusations have existed far into the 20th century, and that would also be the reason why Catholics in the Netherlands were always among the poorest groups, with only limited power, and for long, even limited freedom to practice their faith.