From a reader in the know:

Jonah,
There is a growing body of literature showing the link between expansive public retirement systems and low fertility rates as well as low human capital investment per child. Our current public retirement system, in essence, transfers 10% of the labor earnings of each generation of workers to it parent’s generation. The problem is that each retiree get benefits without regard to the production of their own children or whether they even had children.
Think this doesn’t matter? Try a mental experiment. What if instead of getting money from the working-age population as a whole, each retiree couple got 10% of its own kids’ labor earnings. Some families would have more kids, and almost every family would put more effort into raising them into productive citizens. So putting your kid into day care might make sense now, but what about later on when they might earn less because of that choice? Do you re-model your kitchen or buy a few extra years of private school? Let them watch all the television they want? …etc.