Oh no, not a better job market, more available housing, and less pollution! What a catastrophy!

Flippancy aside, of course birth rates are declining. Of course constant expansion isn't sustainable. The systemic gluttony of capitalism literally cannot go on forever, and the faster we slow it down the better. It's a cancer on our species and our planet. If we want to continue to exist in any capacity we need to get it under control, and that's going to require reconsidering things like constant market growth and never letting the population fall.