Also: SF's refusal to build is having repercussions elsewhere, like here in Oregon where there is a steady stream of people who can't afford a house for their family in the bay area. In turn, they're pricing out people here, and so on.
Also, there's nothing 'extreme' about the population density of San Francisco. Density in Paris is 21,000/km^2 and in SF, 7,124/km^2