Increased public debt and future liabilities (Social Security, Medicare) burden young people and may discourage them from having children because having a child now entails bearing the utility cost of the child's future taxation

Economic theories are based on the idea of expansion and growth of humanity, so if population expansion is about to reverse, the foundation of economic theory needs to be rethought

If we assume that people are now free to have the optimal number of children without prior constraints (high infant mortality, economic need, lack of contraception), then population shrinkage is not a problem but a solution—better for the environment, housing prices, and crowding

With a lower global population (2 billion), we can have a clean world without relying on pesticides and pollutants to support 10 billion, and most environmental damage derives from population density and agricultural chemicals rather than absolute population

The big question is whether fertility decline will be maintained or whether some equilibrium will occur; it seems likely fertility decline will continue because wealth correlates with lower fertility and we do not expect people to become poor

The most important innovation to reverse fertility decline would be artificial uterus technology (uterus for rent), which would reduce dramatically the cost of producing children, though short of that, the opportunity cost of women's time is unlikely to change significantly

There is a tradeoff between risks of too many people (population explosion, environmental damage) and too few people (economic collapse, replacement by AI), with an upper limit (20 billion seems horrifying) and lower limit (extinction is bad), so we must find balance

The majority of people would probably choose short-term happiness over long-term species survival if forced to choose—suggesting humans are biased toward immediate welfare over collective existence

Women's entrance into the labor force has massively increased the value of their time and therefore the opportunity cost of having children, which is the big change driving fertility decline

Germany's development of synthetic fertilizer during World War I dramatically expanded global population capacity; without that discovery, Earth could support only about 2 billion people rather than the current 8 billion.

Women's value of time has exploded historically; a woman at the beginning of the 20th century had almost no autonomy or opportunities, whereas now even wealthy non-working women have a world of options and opportunities available to them.

Pension systems and government debt are structured on the assumption of continuous population growth; rapid population decline creates an unsustainable fiscal burden on working-age people.

Artificial intelligence can substitute for human creativity and innovation that would otherwise require high population; so a smaller human population with AI substitutes is not necessarily a problem.

Once humans broke the Malthusian logic that overpopulation leads to starvation, there is nothing balancing fertility decisions off—if all people decide not to have children, there are no incentives for others to produce more children

Human reproduction is mostly out of the market system—even in the most neoliberal economy, uterus for hire is limited—so the overwhelming majority of reproduction is dictated by the social realm, not the market, yet it has gigantic effects on market economy functioning

Western society is very individualistic and does not think about the species or community as an element, unlike the Catholic religion which emphasizes community and sometimes requires sacrifice, including having children for God's happiness

Fertility is an exponential system, and once decline begins and is maintained constant, population shrinks very fast—like pandemic exponential curves, but in reverse