If a society is required to pay so much for something that used to come naturally through cultural forces, then it’s probably not sustainable.
So much? Singapore's GDP per capita is $60k per year so $5k per month. If $2 month's worth of GDP for 1 baby so an entire lifetime of a new citizen is a lot, then I don't even know what to say.
> for something that used to come naturally through cultural forces, then it’s probably not sustainable
Having kids sucks (your mileage may vary, but before ~2-3 years the investment >>> benefits for all but the most dedicated people out there). Kids used to be cheap labor, which is now illegal for good reasons and they could be abused at will for various things, which is also illegal for good reasons. They were also frequently born because women didn't have a say in the matter, which is also becoming illegal for good reasons.
It is sustainable, it just needs to be done properly and respectfully.
Not by treating women like broodmares and kids as slaves to be worked to death and beaten up by adults who don't have any other way to relieve stress.
The hard truth is that it's not as expensive or complicated to encourage people having child but for some reason we are trying to do anything except for the things that actually matter: allowing parents that want to spend all their time with their new child this opportunity and allowing parents that can't be bothered to handle all the early mechanical aspects to avoid them.
Cheaper starter housing and for the US cheaper higher education would also help but I'm convinced those are lower priority than targeting the early years.