I grew up in the English port city of Liverpool, which received an infusion of tens of thousands of Irish Catholics during the Great Famine in the mid-1800s. The masses of mostly poor Irish who settled the dockland and inner city areas eventually transformed the social fabric of the city and even created its distinctive accent.

A century or so later as a kid in the suburbs, I was surrounded by descendants of these Catholic immigrants, and interactions between Catholic and Protestants came naturally and un-selfconsciously. The only difference Catholics made to my life was that the school cafeteria served only fish on Fridays for lunch. Not exactly earth shattering.

In my teenage years, I soon lost this happy ignorance of the acrimony of discrimination. I learned that there were indeed Protestants in my city whose seething resentment of Catholics was just below the surface, always ready with a cutting epithet directed to the local parish priest or to Rome. And there were Catholics who returned the bitterness, with interest.

It took me longer to learn about the deep and persistent roots of this prejudice, which reached back centuries to the English Reformation and the Civil Wars and persecutions of the 17th Century. Even today, Britain’s head of state is prohibited by law from marrying a Catholic – an extraordinary anachronism in such a bastion of democracy.

In the New World, much of that prejudice was imported and exacerbated by acute competition for jobs and housing in the tenements of New York and other great cities, apart from the contest for souls. The history is too well known to need repeating, and too complex to summarize easily.

Yet it still seems improbable to me that people can get agitated and vent hatred about someone else’s religious differences in a pluralistic society like ours. Does discrimination against Catholics still exist in the U.S.? Undoubtedly, to some degree. Catholics are in a far better position to assess that than a non-Catholic, but I assume they would think it is far less prevalent than a hundred or even 50 years ago.

At any rate, the biggest religious denomination in the nation can pretty much take care of itself in that regard.

The “why” is much more difficult to get at. There is a difference between discrimination and disagreement, but the line isn’t always a hard and fast one.

Discrimination suggests more than deeply held and thoughtful objections to elements of theology or history, or discomfort about the size and power or practices of a global organization. It implies prejudicial treatment of someone because of their religion, especially in matters that are not religious – employment, housing, or social interaction such as how we treat our neighbor or how we express ourselves in public.

Our laws take care of some of that. But laws don’t easily change the way we think, at least in the short term, and the advanced citizenship requirements of our particular kind of democracy demand more of us.

Prejudice is learned, after all. And whatever is learned can be unlearned through education, social interaction, a little effort – and often a good deal of time.