The current population of the planet is well below carrying capacity, look at South Korea and Japan for examples of very high population density, advanced societies. But, If we do exceed carrying capacity that would create a good reason for Mars colonization...
Frankly I'm surprised by how many educated people buy into the Malthusian superstition. Malthus has been wrong for a hundred + years and continues to be.
Increasing population creates economic stability, decreasing population economic instability (though I agree that technology can mitigate this to some degree).
I disagree. We can have large population densities in some places, but a lot of resources need to be gathered in other places to support those people. The large population in East Asian countries has contributed to the massive decline in fish in the Pacific Ocean. Large Asian factory ships scoop up fish from the world's oceans at rates that were unimaginable a couple of decades ago.
Japan and South Korea are net importers of food, as is China to a small degree. Their food needs to be grown somewhere else where the population density is low enough to grow food for export. This problem is going to get worse in the next decade. Both China and India grow a lot of their food with ground water. China has exhausted all their shallow aquifers and are currently using up the deepest water they can get. When those aquifers are exhausted, China will be buying food from the world market and putting a big strain on it. The world is just barely able to feed all it's mouths right now at the cost of fisheries in the oceans as well as straining the farm land around the world.
I also disagree that an increasing population creates economic stability. The countries with the most economic stability are the ones with populations decreasing naturally and the most unstable are those with booming populations. Egypt has seen a massive boom in their population since the 1960s when childhood vaccines were introduced almost universally. Their economy has become very unstable since. They have a massive population of young men with no work and no prospects for work. The Arab Spring happened there (and in other Arab countries) because food prices went up due to drought in Australia, followed by floods in the American Midwest, with massive brush fires that killed the wheat crop in Russia thrown in. Just disrupting the food output from those exporters led to political instability in Africa and the Middle East. That's how close to the edge we are in food production.
And this is just food. An industrialized society like you have in Japan and South Korea consumes more energy, and more of all resources than a non-industrialized society. This is good for factory workers in China, but Western Australia is being strip mined to provide the raw materials for these factories. A lot of other countries are also seeing their natural resources stripped away in bulk. Madagascar was once a heavily forested island with a lot of unique wildlife. Today almost all the forests are gone. The rain forests of South America have also been torn down to open up farm land, build new settlements, and extract mineral wealth from the Amazon basin.
Historically, Europe was barely subsisting when the black death ripped through the population. The plague was so devastating in part because the population was very hungry. There were more mouths to feed than there was food. 1/3 of Europe's population died over a couple of generations, which was horribly traumatic for the survivors. But when the plague was gone, Europe took off technologically and economically. For the first time in centuries, Europe had upward mobility as smart peasants rose to take jobs left vacant by the plague. With a smaller population, the wealth trickled down to the lowest classes better enabling them to live better lives and feed into the economy. Science and technology also got a big boost as people started thinking about improving this world instead of living for the next one. It was probably also boosted by the social mobility allowing people of lower classes with the talent to go into those professions. A number of Renaissance scientists had humble beginnings.
A shrinking population is economically difficult while it's happening. Japan is struggling because they have a large population of pensioners and not that many people to pay for them. However when the current generation of retired people passes on, Japan should bounce back economically and do quite well in the world. Other counties have the same economic bottleneck looming because of the Baby Boom in many countries and the one child policy in China. While the large cohort is retired with a smaller cohort funding them, those countries are going to struggle economically, but everyone will probably be better off in the long run with smaller populations. With automation, we don't need anywhere near as many worker bees as we used to. Machinery can do a lot of what used to be done by unskilled labor. A small population managing machines is economically better than a large population of manual labor.
