You’ve touched upon another of my favorite observations, which is that from a societal and cultural standpoint, procreating is a lot like voting in a U.S. presidential election, in that your individual contribution (or lack thereof), taken by itself, means next to nothing in deciding the outcome. That is, you could have one child or ten, or none at all, and in the big picture that won’t make a dime’s worth of difference. Therefore you have next to zero incentive for giving societal/cultural impact any weight in your family planning decisions.

This is truer in a tax collection/public benefits model than a private one. If you could appropriate the benefits of having ten successful children through an extended family system then your outcomes would be drastically different from a childless, unmarried person’s. While I don’t advocate returning to a clan or tribe system, we should mitigate the averaging out effect of collective social benefits so that a signal is sent to people to do the optimum thing. Without that signal you’ll have the tragedy of the commons.