One common argument against new urban housing runs as follows: “If we build new housing, it will all be bought up by rich investors who will sit on it. So new supply doesn’t restrain housing costs.” This argument (at least as I have phrased it) strikes me as absurd. Here’s why: for the argument to justify restraining supply, the argument presupposes that if you build 100 new condos/houses/apartments, every single one of them will be bought by an investor, and every single investor will irrationally choose to sit on the unit rather than renting it out.