A (relatively weak) inherited instinctual desire to procreate aside, people have kids because it improves their personal outcome. Without modern machinery, the work input of kids will improve the family farm's productivity by more than they consume. With high infant mortality, more kids improves the chances that enough will survive to adulthood. Without modern social safety nets, elders would simply starve or die of…
>The planet's population is getting uncomfortably high, so the birthrate drops. Great. If the birthrate drops, neither you nor I nor the kids alive today will get a "retirement". It'll become a quaint little thing we once could afford. Not so bad if all your work is tapping into a laptop. It's bloody murder for anyone that has to stand and lift and DO for a living.
So long we keep enough skilled tradesmen and farmers, which is not that many with increases in automation, we'll still have enough food, shelter and clothing. Being able to spread that work out amongst more people because bullshit jobs aren't a thing anymore will also probably help, as will changes in lifestyle that enable people to stay healthy longer.
We really don't need a new H&M collection every two weeks, or a new sport jersey every two seconds, or to keep making more and more cars/washing machines/TVs... most manufactured goods (including clothing) can last a while, especially in a world where planned obselence is no longer the norm. If population stabilizes, need for construction drops as well. Food/agriculture is already very automated, I'm sure we can continue to find 3% of the population to keep us fed.
I believe most of the work currently done on earth contributes very little to human happiness, and I hope/want to believe that as our ability to do work diminishes with an aging population, the useless stuff will be the first to go.
silly example, but with GPT-3/ChatGPT, we can now fire all the influencers and have them go toil as construction workers :P