I think you seriously underestimate the depth of anti-Catholic feeling in the US pre-1960, or the degree to which, in the pre-Vatican II world, Catholics in the US were seen and saw themselves as very distinct from the rest of the population. By then not any less loyal Americans (the old charge of dual loyalty had already lost much of its bite by the time Kennedy spoke to the Houston clergy), but with a separate education system and with distinctly different cultural values. I think that if you were able to carefully interview people, you would find that most Protestants born before 1930 for sure, and likely those born before WWII, grew up and remain suspicious of Catholics would have been almost as uncomfortable with their child marrying a Catholic as with the child marrying a jew. Don't get me wrong, I think such prejudice is wrong, but it was quite real.
My father was atheist, and my mother a devote Catholic.
Although, my father’s Protestant relations attempted valiantly to be respectful of Catholicism they weren’t entirely successful.
My brother married a Methodist girl in a Methodist ceremony. None of my Catholic relatives attended, and they shunned my mother and us for a few years. They refused to accept the marriage as even being valid.
Well...By the time I was growing up, Catholic prejudice was waning, and I personally experienced little of it.
My 2 brothers and I were very distressed by the religious upheaval in home due to my older brother’s marriage. Although I attended Villanova, an Augustinian university, I was not then practicing Catholicisms. I have been a faithful member of another Christian religion for 25 years.