I think it will be quite unpleasant for my peers and I if there's not enough working age adults around to produce goods and services for us when we're old.
Because you thought that this trend could have continued for centuries?
We built an economy based on the fact that resources and population could grown indefinitely and now we are surprised that we cannot cope with limits. Looks like we'll have to learn it the hard way.
What's desirable is not population expansion but neither is population collapse, it's population stability.
This also has nothing to do with Capitalism being built for perpetual growth: of course it is deemed to fail at some point in a finite world, but that's irrelevant to the topic of demography. If anything, the system will see the population decline as an opportunity, as it means fewer people to share the resources with.
I think that the crux of the problem is that populations are inherently unstable. There is only one point of equilibrium and that point is very hard to achieve, barring some kind of dystopian tyranny. There are just too many things that influence boom/bust dynamics (world wars, contraception, education, culture etc.)
There is only one point of stability and getting there is like placing a basketball atop of a flagpole.
You don't need exact stability though, having a fertility rate just above or just below replacement rate in periods wouldn't be too big of a deal.
But now we are facing a crisis. For instance the next South Korean generation is set to be half of the current one. And fertility declined strongly there over the past 10 years. Many countries are now at levels SK had ten years ago (well below the replacement rate by higher) and if the trend continue they may end up in the same situation as SK in a few years.
Halving your population over one generation is a catastrophic event.
