Well in this hypothetical, the post-apocalyptic scenario that bankrupts Social Security also renders savings worthless. Having a kid is very robust against something like hyperinflation, lol.

In any case, that solution doesn't scale. Every form of retirement savings is just a way to earmark the production of someone else's kids (so long as human labor is needed for things, that is). If you invest in Google stock in lieu of having kids, you better hope that everybody doesn't get the same idea because then Google would have nobody to work there, and its advertising affiliates would have no working-age people to advertise to.