> If we build new upmarket housing, then upper middle class people move there and lower middle class people stay in existing housing. If the Mission were a cl

> If we build new upmarket housing, then upper middle class people move there and lower middle class people stay in existing housing. If the Mission were a closed population, I would agree with you. However, there's a pool -- or rather an ocean -- of people on the housing market: people in different parts of the SF, people looking to move to the bay, etc. If the upper middle class in the Mission got new housing, I don't see the landlords dropping rent prices so the lower middle class can afford it, when someone from one town over is willing to pay the same or even +10% over their competition. > Building a lot of both is the only reasonable way forward. I agree with you here. I think new housing supply should meet demand across the market. My guess is that _new_ housing supply could be 10x what it is now in the bay. There's something about the housing market in general that's different from typical goods markets. People buying a car don't care as much about depreciation, whereas people buying a house expect it to appreciate as much as possible over time. It's some kind of positive feedback mechanism that counters the typical negative-feedback that lowers price as supply meets demand. There's probably a name for this kind of market but I'm unfamiliar with it.