I have met numerous people and have some friends who are ND football supporters simply because of religion. They have said this to me and I believe it. All that has told me over the years is that there are some Catholics who cheer for ND football simply because of religion. Even with these experiences, I never once thought that there was any type of indoctrination taking place in the Catholic church programming all to cheer for ND. To me, and this may be "arrogant", I never consider these type of supporters to be true fans; it simply gave them something to identify with.
My brother-in-law is an ND graduate. He went there due to religion. His sons are recent ND graduates. They went there by choice, not because of religion. They had their choices narrowed down to ND and OSU, but they grew up in an ND household. So in my family, I have a relative who went there because of religion and 2 who went to ND irrespective of religion. (As a side note, there are a helluva lot of Methodists in this country, yet I have never met an SMU football fan simply because of religion

)
IMO, ND's national fan base has grown over time, or maybe a better choice of words is that it got some assistance, partly due to its affiliation with religion. (Would my nephews have gone to ND if their father hadn't?)Think back to the early 1920's or 1930's. How many immigrants coming to the country, knowing nothing or maybe little about football, hear about ND (the Catholic university) and if the immigrant is Catholic, it gives them something to identify with? I knew one such immigrant in my hometown who fits this description.
With that said, I despise ND more than any other program. But their "true" fans aren't as arrogant as Cryami fan nor scUM fan. And scUM fan who is also an alum is usually the most arrogant SOB around.