The National Council of Churches' 2010 Yearbook of American & Canadian Churches reports the continuing trends of growth in traditional, conservative churches and decline in mainline, liberalizing churches. Catholicism, the largest church in America several times over, grew 1.5%, while mainline Protestantism - Methodists, Baptists, and particularly Presbyterians (down 3.3%) - heavily declined.
The reasons for membership flux are diverse - including immigration, birth-rates, conversions / newcomers and disaffection - yet the aggregate of such factors has long favored faiths which do not sail smoothly with the drift of society.
Of interest, Catholicism is accompanied by relatively unorthodox faiths (Mormons, Assemblies of God) in boasting growth. These denominations share comparatively strict moral standards and demand a great deal from parishioners. That is, they are far more burdensome than mainstream alternatives. And yet they flourish while others fail. To wit, Jack Haberer, editor of Presbyterian Outlook magazine, lamented:
Baby boomers who are also Christians, in general, have been drawn more to churches that are more informal, less institutional and more rock 'n' roll-ish. Presbyterians and other mainline denominations have been very slow in reading those trends and thinking through a way to accommodate without compromising the theological integrity.
They've mastered the first prong - accommodation - though maintaining integrity may be a feat which no amount of thinking will accomplish, if the first prong is inviolable.
Perhaps it is that the very lure of religion is the mysticism and trial involved. In the immortal words of Jimmy Dugan: "It's supposed to be hard. ... The hard... is what makes it great." Further, the spiritual rewards of a profound faith are more likely to retain practitioners than one offering mere regurgitations of Sesame Street, feel-good lullabies. Religion requires leadership, and while pandering to modern mores may pacify lukewarm C&E (Christmas and Easter) Christians, it rather offends the principled convictions of the passionate believer.