Image credit: Aaron Weaver at thebigdaddyweave.com.
You are probably thinking that I'm going to blame the continuing decline on the resurgence of authoritarianism and doctrinal absolutism in the SBC. But there's definitely much more going on. When you look at the broader context of American denominationalism in particular and voluntary associations in general, there is a clear sea change that has taken place. A lot of this story is summarized in Robert D. Putnam's 2000 book, Bowling Alone: The Collapse and Revival of American Community. (Incidentally, I first learned about this book when OBU President Mark Brister referenced it in a guest presentation he gave to my senior ministry seminar in 2002.)
The SBC is not unique in its membership challenges. Other religious groups have suffered the same fate -- many far worse. Demographic shifts go a long way toward accounting for these trends. Another key difference is that people are increasingly comfortable with having "none" as their religious affiliation. Years ago, even if someone had not been to church in years, Americans felt a strong pressure to give some answer when pollsters asked about their religious affiliation. Today it's much more socially acceptable to be unaffiliated, even in the Bible-Belt South.
The lack of brand/institutional/denominational loyalty among the younger age cohorts is also striking. Given increased competition from nondenominational churches in places where likely SBC constituents live (e.g., white suburbs), it's no surprise that the SBC has lost ground.
I would love to blame this all on fundamentalism, but I think it's more important to be intellectually honest. To that end, I think it's vital to point out that there is a growing body of survey data and scholarly research that points to a big reason for why young people are abandoning conservative Protestantism in droves. Hout and Fischer (2002) suggest that politics is a likely culprit. While the proportion of Americans who expressed no religious preferences was unchanged from 1974-1991, it doubled in the decade after 1991 (from 7% to 14%, and continues to skyrocket). Though Americans maintained roughly stable levels of conventional religious beliefs, the increasing politicization (i.e., Republicanization) of evangelicalism has undoubtedly turned many young people away. More recent studies point to the increasing identification of evangelicalism with anti-gay politics as absolutely toxic for retaining younger cohorts in the church. A great deal of recent research bears this out, including Putnam's most recent book American Grace: How Religion Divides and Unites Us (coauthored with fellow political scientist David Campbell).
A few evangelical leaders who are slightly less reflexively pro-Republican have spoken out about the need to liberate the church from partisan politics (Jonathan Merritt and Rachel Held Evans come to mind, and both have taken intense criticism from older evangelical leaders who made their careers, reputations, and fortunes off the culture wars.)
When I put on my Save OBU hat, it's tempting to use the data above to slam the Takeover as driving the SBC's decline. We can blame the Takeover for a lot of problems, but probably not for this one. Since I wear my social scientist hat the other 23 hours every day, I have to refrain from the temptation to let correlation imply causality.