The fallacy here is that the article does not consider the possibility of rising worker productivity. If productivity rises quickly enough, the ever fewer workers could face a future of lower taxes, lower debt, and earlier retirement.
It's also interesting that the Atlantics of the world have gone from "global fertility is rising and we're all doomed" to "global fertility is falling and we're all doomed". I wonder if in between there was ever an Atlantic article stating that global fertility was optimal and we are not, for the next couple weeks or so, all doomed.
Probably not. Doomers gotta doom.