Mmmm…soon as a billion people a year stop piling into Colorado and turning the entire Front Range and Eastern Slope into a suburban wasteland I’ll worry that we’re running out of people to make more people to buy more stuff.
When cultural and economic circumstances make it desirable people will have more children. Attempts by governments to artificially stimulate the production of people is likely to be just as poor an option as government efforts to stimulate production of just about anything. Except weapons and debt.
Why is a declining birthrate a big deal? My impression is that while each individual is a marvel, there is in general a surplus.