>Just to concentrate on food alone: we are barely harvesting anything from the oceans.
Just to cite one of of your statements, the oceans have been decimated with countless species extinct and many more on their way there due to overfishing and habitat destruction. The oceans are also filled with industrial chemicals, plastics and have numerous massive "dead zones" due to nitrogen run off from the huge factory farms we run to sustain our massively overpopulated planet.
The suggestion that the earth isn't overpopulated, let alone the idea that the earth could support "hundreds of billions of people" is beyond absurd. We are losing biodiversity among animals, insects, fish and every other form of non human life due directly to massive overpopulation. Saying this ignores the decimation of our ecosystem and the food web that has left our planet teetering on the brink.
You are right that we are past what hunter-gatherer approaches can yield from the ocean. And that we are doing a bad job at protecting the habitat of wild-life.
However, there's vast patches out in the open ocean where almost nothing grows. Mostly because the areas with sunlight (at the top) are not where the minerals are that plants need to grow (mostly the sea floor). See eg https://en.wikipedia.org/wiki/Iron_fertilization for an overview.
If you mind putting fertilizer directly into the open ocean, someone more clever than me can probably work out a scheme for enclosing some water in a giant floating bag, and growing your stuff in there. (Or something much better than this.)
Just to cite one of of your statements, the oceans have been decimated with countless species extinct and many more on their way there due to overfishing and habitat destruction. The oceans are also filled with industrial chemicals, plastics and have numerous massive "dead zones" due to nitrogen run off from the huge factory farms we run to sustain our massively overpopulated planet.
The suggestion that the earth isn't overpopulated, let alone the idea that the earth could support "hundreds of billions of people" is beyond absurd. We are losing biodiversity among animals, insects, fish and every other form of non human life due directly to massive overpopulation. Saying this ignores the decimation of our ecosystem and the food web that has left our planet teetering on the brink.