1. Make the city suck
2. Get the housing vacancy rate to 5.5%
And of course he says this to encourage everyone to work toward #2, and the way to do that without displacing anyone is to build new housing.
I don't really understand the opposite logic, which the NIMBYs like to use, saying that building new housing will drive the price up.
I mean, I am not some kind of libertarian free-market cheerleader, but it shouldn't be that controversial to say that a market exists, that the way to bring down the price in the face of overwhelming demand is with supply.
People point to how expensive newly-built market-rate housing is, but that's a symptom of the shortage. People want to live in good cities. If there's not a new home for them, they'll pay even more for a home someone lives in, so prices go up and a community gets displaced.