On Monday I cross-posted on Mirror of Justice and Religiousleftlaw about those who have left the Catholic Church. Several of the comments at Mirror of Justice wondered or made assertions about the relationship between Catholic losses and mainline Protestant losses. A general perception is that mainline Protestants have lost members in greater percentages than Catholics. I think that perception is correct, but the relationship is somewhat complicated as Putnam and Campbell detail in American Grace.
Fewer than half of Anglo Catholics and mainline Protestants raised as children in those traditions remain observant members of their faith and the differences in percentages between Anglo Catholics and mainline Protestants are not significant. Conversions to Catholicism or mainline Protestantism are not significant enough to make a dent in these losses. (The average age of Catholic converts is 65. Putnam and Campbell speculate that these converts were primarily the product of non-Catholics marrying Catholics years ago).
Catholics have partially offset their losses with birth rates that are higher than mainline Protestants. (Some sociologists maintain that the main cause of mainline Protestant decline is low birth rates – I once heard Robert Wuthnow give a presentation at the American Academy of Religion in which he attributed 90% of the loss to low birth rates. Putnam and Campbell do not think low birth rates explain as much of the loss as do other socilogists).
But Catholics have mainly offset losses by Latino immigration. Without that immigration, American Catholic membership would be in very substantial decline. Indeed, Putnam and Campbell maintain the transformation of the American Catholic Church “from a largely white ethnic church to a largely Latino organization is inexorable.”
If one looks at the American Catholic as a whole, as opposed to focusing on Anglo Catholics, I am sure that the percentage loss in membership turns out to be greater among mainline Protestants than among American Catholics, but I do not yet know what the percentage difference is.
I have yet to discuss the different reasons why Catholics and mainline Protestants leave their faith traditions. More on that later.