We can’t let everyone choose to live in the same place. There has to be some mechanism, hopefully market-based but it could also be a residency system, that ensures people spread out and live in different places. Even if you could get SF to support a billion people in living space, I’m sure infrastructure and resources like water would cut things off before it got to that many people.
There absolutely does not have to be in mechanism to spread people out. It is cheaper to provide infrastructure to people who are much closer together than it is to provide the same infrastructure to people who are spread farther out.
There's been a website for the last 20 years called Strong Towns that talks about this a lot if you're interested in learning more.
Building up isn’t cheaper at some point. Around 30 stories is the economic limit right now when you consider fire safety, with anything higher reserved for splurges.
Having lived this in China, the economics get wonky in dense cities. I’ve never seen the built up area with lots of 30 stories being cheaper than 4 story blocks. And that is in the most zone-agnostic build happy country on earth.
