the issue is that our current socio-economic system is designed for population grown. it could maybe survive population stagnating and the demographic pyramid becoming a demographic column, but it can't survive a demographic pyramid inversion, which is what is currently happening everywhere. it is a demonstrable fact that our current systems for taxation, welfare, etc depend upon there being more people paying into the system than there are dependent on it. the way our economy works, there needs to be competition in the labor market to keep wages "affordable" (read: low) for businesses that operate at scale, across many local economies where the cost of living varies. basically our current society is meant to function with lots and lots of people and the assumption that there will always be more people.  nobody has bothered to design a new system for two reasons. the first is that people currently in power have no reason to upset the status quo when it is the reason they are in power. the second is that short-term thinking has pervaded every aspect of neo-liberal world order for the last half century. focus on the immediate situation is what has driven corporate culture, and it's what drives politics even at the national level. people capable of thinking about the long-term, and executing a plan for it, are extremely rare these days, and they are not popular or influential figures in society at large. what all this means is that yes, a smaller population as a concept isn't a bad thing. but our populations are not going to magically shrink by a third or half, while maintaining a healthy demography. the demographic pyramids are going to invert, there will be many more old people than young, causing the tax base to implode, government programs to collapse, and a great deal of chaos as a massive shortage of skilled labor and experts sends shock waves through high tech, medical, and engineering fields.
United States