Then show me it's wrong.
The Catholic Church's position on birth control hasn't changed in over 2,000 years; the Protestant position changed after 400.
By migrating to a Protestant country, Catholics exposed themselves to the dominant culture, which was, of course, Protestant. And when the Protestants practiced birth control en masse, the pressure (financial and societal) on the Catholics was simply overwhelming.
Does it excuse Catholics for giving up the Faith? Absolutely not. Is it the fault of the Protestants that the Catholics joined them? Certainly not. But if anything I've said here is incorrect, then correct it.
Natural. Family. Planning.