...The decline in membership of mainline churches over the last century had more to do with sex than theology, research by a trio of sociologists suggests.From the Institute for the Study of Labor:
The popular notion that conservative churches are growing because mainline churches are too liberal is being challenged by new research that offers a simpler cause for much of the mainline decline--the use of birth control. Differences in fertility rates account for 70 percent of the decline of mainline Protestant church membership from 1900 to 1975 and the simultaneous rise in conservative church membership, the sociologists said.
"For most of the 20th century, conservative women had more children than mainline women did," three sociologists--Michael Hout of the University of California-Berkley, Andrew Greeley of the University of Arizona and Melissa Wilde of Indiana University--wrote in Christian Century...
...During most of the last century, more people moved from mainline to conservative churches than in the other direction. Conservatives were much more successful at retaining their church members, even when they married mainliners.
"The declining propensity of conservatives to convert to the mainline accounts for the 30 percent of mainline decline that fertility rates cannot account for," they concluded.
The researchers investigated other possible causes for mainline decline--support for homosexual and abortion rights, a lower view of the Bible, a higher "apostasy" rate, and fewer conversions from outside the Christian fold. But they dismissed these other factors as irrelevant because none could produce numerical changes significant enough to explain the shift in church membership.
"Higher fertility and better retention thus account for the conservatives' rising share of the Protestant population," they concluded...
...Some religions provide psychic and social rewards to those who have many children, in the form of approval, social status, and blessings. As Stark and Finke (2000) have noted, the high fertility that Mormons have consistently displayed in the United States (Thornton 1979; Heaton 1986; Lehrer 1996a) can be interpreted as a rational response to such incentives. Similarly, the Catholic religion embodies strong pro-natalist ideologies, which raise the perceived benefits of having an additional child. It also has teachings that forbid artificial forms of contraception, oppose abortion, and increase the costs of family planning (Sander 1995). Until the 1970s, these norms had been manifested in a distinctive pattern of very high fertility. More recently, adherence to the teachings of the Catholic Church in these areas has weakened markedly, with a corresponding decline in family size (Jones and Westoff 1979; Mosher et al. 1986; Goldscheider and Mosher 1991).1 Some aspects of conservative Protestant ideologies are also pronatalist, and the fertility of this group has been found to exceed that of mainline Protestants, but only by a small margin (Marcum 1981; Lehrer 1996a).From C. Kirk Hadaway, Director of Research, The Episcopal Church Center:
...In addition to race and ethnicity, educational attainment and family income are highly related to the birth rate. Not surprisingly, American women with a graduate or professional degree have the lowest birth rate, followed by women with Bachelor’s degrees. Also, women in families earning $75,000 or more have very low birth rates, as do women in families earning $50,000 to $74,999. The Episcopal Church has the highest proportion of members among mainline denominations who are college graduates and in households earning $75,000 or more. As a result, the birth rate among Episcopalians is much lower than the national average—and even lower than the population of non-Hispanic whites. A reasonable estimate, based on education and race, is approximately 1.5 children per woman (compared to the replacement level of 2.1) for Episcopalians.As the above quotes should make clear, Bishop Katharine was not making this stuff up.