The posts I've seen here by Maxwell seem to have very high confidence in a conclusion based on a single reason, without considering factors that may have opposite effects or engaging with common arguments by opponents. I'm not exactly a "degrowther" but I don't think this post is contributing to discourse about that, because:
So if current fertility trends continue, gentle degrowth is the default result.
That’s only a short term trend and even then, assumes we don’t get AGI magic. Pronatalist belief systems that persist in modernity (Judaism, Islam) will continue replicating and replace most people. We might even see genes that make people want kids or not use birth control propagate.
“Actually, the problem in the world is that there are too many rich people.”
Degrowth is an ascendant cultural and political movement. Its central claim is that the growth of humanity’s population and economy is unsustainable on a planet with finite resources. Therefore, the only way to avoid inevitable future collapse and incalculable damage to the earth’s natural environment is to voluntarily slow and reverse this growth now. The cultural values and policy prescriptions of degrowth are shared by prominent political activists, scientists, and world leaders.
I’ve written several posts on this blog about low and falling global fertility. I’ve always framed low fertility as a big problem, as indeed it is from a Progress Studies perspective. If you care about continuing the economic growth and technological progress that has created the modern world, low fertility is a massive challenge.
From a degrowth perspective, low fertility is a blessing. Paul Ehrlich helped India forcibly sterilize millions of women. A massive human rights violation, but one he saw as justified given the grave dangers he foresaw with high population growth rates. Today, India’s fertility rate is below replacement for completely voluntary cultural and economic reasons and the global average isn’t far behind. Within the framework of degrowth, sub-replacement fertility and the shrinking economies that come with it aren’t problems to be solved, they are the necessary adaptations to global environmental limits.
Consider how these different perspectives would react to this paper by Chad Jones: The End of Economic Growth? Unintended Consequences of a Declining Population.
A total fertility rate slightly above 2 and one slightly below 2 is the difference between an exponentially growing population and an exponentially declining one. In his paper Jones shows that when you plug in exponentially declining population into the standard models of economic growth you get the Empty Planet Result:
Economic growth stagnates as the stock of knowledge and living standards asymptote to constant values. Meanwhile, the population itself falls at a constant rate, gradually emptying the planet of people. This outcome stands in stark contrast to the conventional result in growth models in which knowledge, living standards, and even population grow exponentially: not only do we get richer over time, but these higher living standards apply to an ever rising number of people.
This is a tragic loss if you believe in the potential for future growth over thousands of years and trillions of human lives, but for degrowthers this is close to ideal. Stagnating living standards isn't a rosy picture but it's far from apocalyptic and that is the inevitable endpoint of growth in their view. Sub-replacement fertility means per-person living standards grow slower and slower until they stagnate, but they never fall even as the population shrinks.
The standard models of economic growth predict that humanity can shrink its size and influence on earth with gentle, managed decline. When Jones integrates fertility choices into his model he finds the standard result that people underinvest in fertility because they don't internalize the benefits their children may create by discovering ideas which improve the living standards of the whole world. But he also finds that even an omniscient social planner can be trapped in the empty planet equilibrium if fertility is too low for too long. The intuition behind this result is that kids are a positive externality because they can produce ideas and ideas are valuable because they can be copied and used by everyone in society at once. But if the population gets too small, this non-rivalry of ideas isn't that valuable because it only applies to a small population.
So if current fertility trends continue, gentle degrowth is the default result.
For those who do see stagnation as a tragedy, this fact ought to be worrying. Not just the fact that progress will halt, but that this might be a gentle process. Facing the prospect of boiling alive is bad enough but sitting in a pot whose temperature increases slowly in comfortable increments makes it much less likely that we’ll jump out in time.
There is no guaranteed wakeup call from fertility decline. The already influential philosophy of degrowth is not guaranteed to face some crisis which is unexplainable within it's framework that shocks people back to understanding the importance of growth. Even if some shock does come which is not modeled in Jones’ paper e.g political collapse due to debt-funded pensions for top heavy population pyramids, it may come too late to reverse the decline.
Disagreements over the value of fertility are inextricable from disagreements over the fundamental value and possibility of progress itself. There are no degrowthers who think that low fertility is a big problem and there are very few who believe in the possibility of continued growth who do not want fertility to increase. Therefore, the general case for progress needs to be a cornerstone of fertility advocacy if it wants to change the minds of anyone who is not already primed to agree.