Germany has some of the best youth employment numbers (see chart at https://news.ycombinator.com/item?id=27393190) and yet birth rates are similarly low.
Germany has issues as well, even though that specific statistic looks good
Even with all the incentives (subsidize childcare etc.) you'd still have to modify the harder to modify cultural reasons like people valuing independence, "casual dating"/FWB relationships for years that go nowhere is more common instead of dating with intent to marry, hustle culture/emphasis on career progress, less social pressure/shaming from parents ("why don't you have a husband/wife/kids yet?!"), freedom to "find yourself/travel" or "get sexually experienced/have a ho phase before settling" for years after college, etc.
Most people don't want to go from college to marriage and kids right away these days, and a few years of this type of casual dating/exploration after college eats up a lot of prime reproductive years. But these cultural factors are very hard to change especially with the absence of religion/strong communities these days.
Social Security in the US is one example. It literally depends on having a larger input base than the output.
The expectation of GDP growth is another, but without population growth, it's unlikely to be realized perpetually. I'm fine with that, but our over-leveraged financial system isn't.
Do it like software: if the implementation doesn't match reality, fixing the implementation is easier than trying to fix reality to match the broken assumptions
― George Bernard Shaw, Man and Superman
But if you believe it is reasonable or desirable to engineer social changes to increase the birth rate to be able to create and support economic growth, I think your priorities ordering is not right
2. Economic growth can be driven by increases in productivity. Automation can massively boost productivity. But at a certain amount of supply of labour, it is cheaper to employ a human than automate the task, even though the automation technology for that task is within reach. So a reduction in supply of manual labour can actually make the economy more automated and efficient.