> "But the deeper reason is that there’s really no such thing as a natural resource. All resources are artificial. They are a product of technology. And economic growth is ultimately driven, not by material resources, but by ideas."
Arable land - i.e. topsoil - is not a product of technology, it's a product of geology and biology, namely the erosion of rocks and the accumulation of biomass. Yes, one can indeed make an artificial soil-like system (hydroponics), but this in turn requires raw materials (typically clay pebbles, plastic pots, plastic pipes, plus a complete nutrient mixture of simple chemicals) which are in turn made from limited material resources.
Similarly, fresh water is a limited natural resource, and in the absence of water, human populations do not grow. Just look at a population density map of the United States - note how few people live in the desert zones. Again, there are technological approaches: desalinate ocean water, pump it to the desert, and grow food hydroponically. This requires an investment of material resources and energy.
I get this feeling that economimsts who makes these claims about infinite growth have simply never studied the conservation of energy, or the conservation of mass. Every source I've looked at puts the minimal land area for food production for one human at about two hectares with traditional agriculture, and maybe half that with modern industrial double cropping methods. US farmland is about 166 million hectares, so that sort of fits, as the US population is about 330 million; exports of food also appear to match imports of food so that's a wash.
So clearly there are limits on the growth of the human population on a finite planet. If the question is, "can you have infinite economic growth with a fixed human population", well, whatever discipline makes claims like that is one entirely divorced from physical reality. Inflation maybe?