I got this via Pandagon as a response to the argument that we need high birth rates to maintain social security:
But without denying that the effect is real, this strikes even a lover of Social Security such as myself as a pretty unpersuasive reason to explicitly target higher birthrates as a policy objective. If it’s true—as I’m inclined to think it is—that slower population growth rates are likely to increase average living standards then people could still be made better off even with smaller transfer payments. Alternatively, a developed country that did find itself in desperate need of additional workers can always let more immigrants in.
Also, if you only have one kid chances are inheritence will be larger, after all you wont be splitting it amongst multiple siblings and by only having one kid you may actually save more money. Who knows people might even be able to afford college for their one child rather than having five of them start their adult life deeply in debt.