clipped from: newsweek.washingtonpost.com   

I think the penchant to change religious affiliations in the United States has to do first with the fact that we have become a mobile society and, second, with the economic and educational achievements that drive mobility.

Traditional religious forms, whether they are Protestant Evangelical Fundamentalism or
Conservative Catholicism are particularly strong among people who do not stray far from family roots, geographically or emotionally.

I do not, therefore, think that it is proper to characterize this transition as either good or bad for American religion. It simply is a fact of life. Religion in this country has always combined tribal thinking with cultural upheaval and social amalgamations.
By tribal thinking I refer to the fact that the ancestors of most Roman Catholic Americans come out of Ireland, Italy and Southern and Eastern Europe. The ancestors of Presbyterians come primarily out of Scotland.
The ancestors of Episcopalians come out of England