People who are trained to see things economically sometimes have a hard time understanding why it might be bad if people stop having babies. Sure, GDP will shrink, but would per capita GDP actually go up? And just imagine the effects in 20 years on the unemployment rate and on wages when you no longer have more workers than jobs.
The concept that best gets economists to worry about a birth dearth is the “old-age dependency ratio.” From a fiscal viewpoint, this is the number of people paying into Social Security and Medicare versus the number of people relying on it. If that ratio gets too low, things could get ugly.
But there’s a more fundamental imbalance here: A society needs people to work in order for people to have things. Fewer farmers mean less food. Fewer truck drivers mean you and your local corner store can’t get stuff. Fewer busboys mean shorter hours at the local diner. We all have tasted this during the pandemic.