Rod Dreher: Reason on the baby bust

Is the conservative narrative on fertility decline (which is, I think, secularization leads to fertility decline) correct? Does it give the primary cause at least? A transformation of culture, as people tainted by sin make use of tools to curtail child-bearing? (In the name of 'being responsible'?) Other than for "serious reasons," how could parents say one or two "is enough"? What has caused dropping fertility rates in developing countries? (Advocacy of contraception by both government organizations and NGOs?)