I would also argue that plenty of people that go for children who are not ready for it don't make it just fine. More importantly, their children, that didn't ask for any of it, end up suffering because of their mistakes. Plenty of people have psychological issues of various degrees because of poor parenting. 15% of families in the UK are lone parent families! By age 12 a staggering 40% (!) of children are not living with both birth parents! [1] And these figures are almost twice as bad for low-income families. And out of the children that do live with both birth parents, 11-28% of the parents report an unhappy relationship. That is the catastrophe.
Humans have this strange blindspot where they tend to be irrational and irresponsible about the decision to procreate. Previous generations did not have much of a choice because of lack of available contraception, lack of knowledge. Our generation has no excuse.
[1] https://assets.publishing.service.gov.uk/government/uploads/...
Secondly, I don’t think your data on single parent families really disproves anything, specifically because that data is highly confounded by drug addicts, high school dropouts, unwed couples, accidental pregnancies, and dozens of other factors. If we’re to reason in good faith, the advice I and others are advocating for is that you don’t need to be a homeowner with a 200k+ salary, although of course you should be a reasonably mature, employed adult with a mature partner.
I think it’s in poor faith as well to reduce this to “if you feel a need to have children, you’re irrational and still stuck in go-forth-and-multiply mode”. But, again, this is not an issue anyone can find common ground over with reason or data (which you can find to support any conclusion), and I expect the HN crowd falls on a particular side of this on average, so I won’t argue further.
The problem is the transition to this lower population. You’d have a period of 40/50 years where older people severely outnumber those who are relatively young, leading to massive increase in per capita healthcare expenditures coupled with a decrease in productivity. So no, at least bot in our lifetimes.