Patrick Boyle has looked at causes of decline in the total fertility rate around the world and concluded reduction in the formation of couples (married or not) is a major cause.
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I'm worried a lot about the declining rates of marriage and family formation. I don't see a lot of good that can come from it.
Dowries vs. free, monogamy vs. polygamy, common law marriage vs. ceremony, wives being property vs. independent people, self-determined vs. marriages arranged by parents, and this biblical passage:
"Moses told us that if a man dies without having children, his brother must marry the widow and raise up offspring for him" (NIV, Matt 22:24)
And it's not like no country has implemented mandatory childcare payments outside wedlock.