The social conservatives consist largely of members of the evangelical churches - including the Mega-Churches. The grandfather of the evangelicals is the Southern Baptist Convention (SBC.) Those churches have been a key element of the conservative political alliance over the last thirty years, and their continued expansion is a part of the myth that the conservative movement is growing.
Well, the SBC is not part of the movement that is growing in numbers. The Reuters article entitled "Southern Baptists (and Republicans): old, white and in decline?">Southern Baptists (and Republicans): old, white and in decline?" reports that the SBC is declining in membership just as has been the case for the mainstream and much more liberal religious denominations they oppose.
The reason why most people that I know join a religious denomination other than the one they grew up in is that they have children and are looking for some way to connect to society in a society that is super commercial and frankly, anti-child. But Christianity does not do a very good job of providing a cultural connection for members, either. That explains the decline in the mainstream religions. It appears that the SBC, the source of some of the greatest wackinesses in the last few years, does no better that the Episcopalian or Presbyterian or other mainstream denominations. It is a common symptom in all three of the major desert religions out of the Middle East (Judaism,Christianity and Islam.)
When the various forms of idolatry (including declaring the Bible Holy and worshiping it as the evangelicals do) cease to satisfy the need for connection to the culture ("cultural roots") there is nothing else to hold the members besides the demand that they not lose their Faith under the threat of becoming ostracized by the rest of the membership. Acceding to those demands mean that you are abandoning all true religious curiosity.
The evangelical attempt to enter politics and take sufficient control of the government to use it as an evangelical tool that started with the televangelist Pat Roberts and with Jerry Falwell and Ralph Reed of the Christian Coalition early in the Reagan regime had essentially failed by the late 1990's when Ralph Reed abandoned the Christian Coalition and went off the do well for himself in politics. Roves mobilization of the evangelicals behind George W. Bush together with a new band-wagon effect gave a temporary rejuvenation to that effort, but the returns from being Republican foot soldiers was never worth it. It's effectively over now, and the only real draw for the evangelical churches remains a being a home and culture for families with young children. The decline of the SBC shows that. The actual membership of the mega-churches is generally far below the membership numbers they announce in public.
The exception to the decline, if there is any, will be in relatively isolated rural communities which have few social resources besides the church. Sarah Palin is the product of such a rural location. But the authoritarian nature of such religious organizations is not likely to hold on to a mobile population that can easily get a job in the city down the road if they become dissatisfied at the current location.
As long as the evangelicals can't get control of government in order to use it to enforce a monopoly of religion and to evangelize, they will continue to decline.
As a society, though, we really need to do something to fill that great yearning need for a connection to the culture. It's not a commercial need, so private enterprise cannot make a profit by filling it. Thus, we need to develope non-commercial ways to fulfill that need for connection and to build a better and more inclusve community. Racists need not apply. With our highly mobile population, the solutions have to be color-blind, race blind, and very inclusive of a variety of cultures and backgrounds.
No large nation other than America has a historyof diversity that will make such solutions possible.