> They can be purchased by the rich to be used as unlicensed hotels aka airbnb. They can be ought up as "investments" and not effectively rented out effectively enough as long as you don't build so much you literally flood the market.
There's a natural floor to this though. For example, if Boston built 3 housing units for every human being on the planet, there would hardly be any problem even if every person wanted to live in Boston and own multiple units. This is obviously absurd, but hints at the greater point. There's a point along the supply/demand curve where prices will end up falling, no matter how much external demand or AirBnb rentals come into the area.
The argument I think you're making is that there's no way to build enough housing units in a reasonable amount of time to meaningfully affect non-upper-end housing. There's not much controversy about that in practice (though weirdly enough there is a lot online.) California (and many Californian cities sweeten these deals) specifically offers developers many benefits for varying percentages of affordable housing mixes in their units. Boston also seems to have income-restricted housing as well. Most pro-housing policymakers agree that housing isn't just a build-build-build game but that incentives need to be offered to ensure affordable units are built along with upper end luxury housing.