[overtomanu]

My theory is that, as of now population might be above a "equilibrium". Since it is above equilibrium, it causes increased economic competition to raise kids. So only few economically well off couple have kid's.

After few generations, population comes back to some level where economic competition to raise kids is reduced. Also, most of the lineages of people who chose not to have kids would have been wiped out or atleast somewhat reduced (Natural selection at play). So the people living in the future are likely to have kids on the condition that there is no economic penalty.

So humanity extinction due to demographic decline is less likely. Instead it might happen due to something like nuclear war. More details: https://en.wikipedia.org/wiki/Fermi_paradox#It_is_the_nature...