If the country didn't go through hyperinflation or a devastating war, then your point is simply wrong.
You are falling for the framing that benefits are "paid for."
That is simply a canard.
Benefits are always a transfer payment.
When people say "social security is going bankrupt," what they are pretending is that social security/social welfare is something where one pays for one's own benefits, which is a total lie.
What they really mean is that rich old people do not want to pay taxes to benefit poor old people.
Every other possible "interpretation" is a fabrication.
Proven to be totally false in every single country where birth rates plummet.
Europe and the Soviet Union gave extravagant benefits to families and mothers to encourage extra births but it accomplished very little.
The reason for falling birthrates is primarily due to the time it takes for females to become highly trained labor for the economy, which significantly eats away at the time they are the most productive producers of healthy non-inferior offspring, which is shortly after puberty till about age 25.
