> Some forms of pollution are more critical than others.

Definitively not CO₂... It was chosen just because we can lower it, while we can't with other pollutant...

> We had such an economy. Turns out canal and then rail are far more efficient at moving goods than roads. So much so that canal and then rail hubs became important towns and cities.

That's a VERY interesting point: back then being in a certain place means live better than some other places, so people concentrate. Now? Allow me to quote a little bit more talking about stocking foods, yes it's possible everywhere there is room to store. In dense European cities there is no room for significant storage, the more a building is newer the less space it offer. We start to see people looking for OLD buildings to have more room just to WFH in hybrid (absurd) setups. And that's pose another issue: in dense EU cities there is no room to evolve. Try Google StreetView in some cities of the center and south. How can you rebuild a building without road access (YES, in some large EU cities some "poor housing" was built in the '60s with ONLY stairs to access on the side of a hill with a single road, lately they added some lift, but still NO ROAD nor no room to make one). How can you even plan to demolish a building where such activity demand to relocate 100+ people and blocks few roads FOR MONTHS in places so dense that there is no alternative path or there are very few and obscene?

I do not know enough USA average situation but in center and south EU cities are dead, there is no way to evolve them behind relocating their resident and rebuild them from scratch a thing so expensive nobody even imaging it, and since relocation is needed anyway better to build something without such horrid evolution problem.

Now on economy of scale: what's produced these days in cities? In EU and I bet also in USA on average almost NOTHING. IN the past cities was the place where all artisans go, so where there is competition, and the innovation, low price and specialization. Now only few giants produce, all the rest resell their goods directly or use their machines to produce something with the raw materials the giants supply. We have reached the point of having restaurants without kitchens, they got a different menu per day, packed often pre-heated food on time, they just serve it. We have dishwashers of some vendors made to "work best with our dishes" and so on. That's why I say there is no more economy of scale.

> Even on a physical level, big cargo ships are much cheaper per ton-mile than smaller ones. That's why we have 20,000 TEU+ container ships.

Sure they are cheaper, but they are JUST A PART of a logistic chain. They are cheaper IF there is a mass production, mass shipping, mass unloading in a restricted area. Actually such cheapness is unsustainable. Did you remember the "panic" where the Ever giver stranded in the suez Canal? In IT terms the name is SPOF.

The idea of the world as a factory, just-in-time productions etc have proven to be cheap WHEN ANYTHING GOES WELL, and a damn disaster when anything break even a little bit. A civilization can't take such risk. That's why we see back in fashion the self-sufficient model, witch alone can't work either, NK Juche policy as a good example. Ancient Roman's have a proverb in medio stat virtus (in the mean lie the virtue), witch means we can't be self-sufficient, and we can't be all specialized in a just-in-time giant factory. We can't be in the contryside nor in city. We need a mean way, that's the Riviera model.