The real reason for the rise of American conservative churches?

I ran across this article in Christianity Today which had a thought-provoking examination of the underpinnings of this growth. The dominant view is that ideological strictness has been the reason. However, dissenting sociologists point to a different underlying basis: demographics.

Earlier I also ran across a paper in PDF format titled "Growth and Decline of Religious Subgroups" by John Hayward presenting systemic models for growth via conversion, starting off with a simple model of unlimited enthusiasm, then elaborating by accounting for births and deaths, reversions, then finally the impact of lessening zeal over time. The simulations and the resulting diagrams are illuminating, and in my view provide additional plausibility to the demographic hypothesis. Show and tell, right?

The logical consequence of this model is that social conservatives looking at the big picture should consider supporting gay marriage or civil union. If the liberal reproduction rate is diminished, then conservatives gain a demographic advantage and will rise in relative influence in a few generations.