Why would you take a mortgage, probably the biggest investment in your life, if you don't plan to have kids? Even in places where its actually cheaper to pay mortgage compared to renting there are so many negative aspects to committing to strict payment regime for next 20+ years to a single place, that it doesn't make any logical sense.

In no kids scenario is much better to rent, adapt your place of live to your current situation/market/plans, when retiring just move someplace dirt cheap and awesome.

If you have kids, its a huge value that you can pass to them, if done smartly (if not, it will probably destroy offspring's relationships between them for life).

I'd like to see data on fertility rates compared across all the socioeconomic space, over time.

I suspect you're not much different than most people: they may want/desire children but due to the ongoing economic climate, are forgoing children. That trend would be a bit more evident if most those in the higher socioeconomic were comparatively either increasing fertility rates or remaining relatively constant over time to those at the lower end of the spectrum. There are of course many other factors to look at but that would be a good start.

If fertility rates across the entire socioeconomic spectrum is at a reasonable decline, then overall (assuming there isn't some huge epidemic we're unaware of), it's probably a good thing. Population saturation points should not be artificially set by our current economic system since it's pretty flawed across the board in most aspects, I can't imagine its a useful constraint for determining genetic diversity and growth for humanity.

I wouldn't. But fortunately for us, our ancestors did.

To pay for a social safety net.

People do adapt, situation does get better. You can afford a mortgage, that is huge. Most people are not lucky to have their own shelter and they are renting.

Noone said child is an economical decision. It is the worst economical decision in fact.