> The assumption that if we don't incentivize new births the conomy will collapse is just an assumption
Not really:
https://www.forbes.com/sites/kenrapoza/2017/02/21/chinas-agi...
The economy might sort itself, but society has a much harder time of it.
Also, there's a class discrepancy in childbirth. In many affluent countries - as you've rightly pointed out - those who can live off what paltry state benefits exist (or even see the childbirth benefits boost their incomes) will - and will procreate abundantly, relying on the state. But quite frankly, those with limited access to contraception and the work-shy will procreate anyway, whether the state boosts their income or not.
Those with mortgages and careers and high IQ will not. Not that IQ is necessarily genetic, but it does tend to run in families.
The kinds of people who engage with HN are probably the kinds of people we should be encouraging INTO childbirth, not out of it - for the sake of society as well as for the sake of the economy.
And yes, there are limited resources. We need to deal with that. I don't think space travel or the next advance in GM is going to fix it all, by any stretch. We should do serious research into how to best fit the resource at hand, as a species.
But high-brow fear-mongering is the worst solution pragmatically. And parents with babies dying in the streets is the worst solution morally (and hygienically). You clearly have some intelligence, so don't settle for the false economy of unfeeling intellectualism, it's counterproductive. Find real solutions, not rhetoric.