Birth rates have a much larger effect on society than I think people realize. I recently read
Shall the Religious Inherit the Earth? by Eric Kaufmann. It makes a pretty strong argument that contrary to the widespread assumption that everyone will just become an atheist, the world will actually become more religious, almost entirely because of birth rates.
In this 2010 book, Kaufmann argued that the answer to the question raised in the title is in the affirmative because demographic realities pose real challenges to the assumption of the inevitability of secular and liberal progress. He observed that devout factions tend to have a significant fertility advantage over their more moderate counterparts and the non-religious. For instance, white Catholic women in France have on average half a child more than their white secular counterparts while the Amish in the United States have three to four times more children than their fellow Christians on average. Highly religious groups tend to isolate themselves from the secularizing effects of modern mainstream Western society, making it more likely that the children will retain their parents' faiths. At the same time, secular people generally have rather low fertility rates by comparison for a variety of reasons, such as materialism, individualism, the preference for the here and now, feminism, environmentalism, or general pessimism. Kaufmann projected that secularism will have a mixed future in Europe. It will remain strong in most Catholic countries, notably Ireland and Spain, but has essentially ground to a halt in Protestant Europe and in France, and will falter in Northwestern Europe by mid-century. He told Mercator Net that the only way to buckle the trend involves "a creed that touches the emotional registers", which "can lure away the children of fundamentalists" and "a repudiation of multiculturalism." He suggested that "secular nationalism" and moderate religion associated with the nation-state could be part of the mix, but these traditions have been losing support at a considerable rate.
He observed that moderate faith of the Abrahamic variety is under pressure from both secularists and fundamentalists as they find themselves living in the secularizing societies of the West.[13] If it were only true that the religious were having more children than secular people, Kaufmann argues that the effects of the incoming demographic transformation would only be national, but because those who are having the most children tend to be intensely religious, he predicted that there would also be ramifications for international relations. However, Kaufmann rejected the increasingly popular notion that Islam will become the dominant religion in Europe by the end of the twenty-first century. Rather, Muslims would stabilize at around a fifth of the European population by 2100.