It's very difficult to build a city to serve two populations, one rich and one poor (or at least average). I would love to work in SF but have zero desire to live there because it's too expensive for everyone but the IPO crowd.
As a resident of a growing city, I find it somewhat puzzling and inconvenient that it's taken as an article of faith that large city growth is a good thing. Growth is good, but it's also bad: it brings congestion, filth, and higher housing prices. Even with the development of affordable housing, housing prices still rise. Furthermore, the traffic associated with high-density houses places a strain on the transit system and other public infrastructure and services that the city is usually unequipped to handle. Transit is often upgraded far too late, long after congestion has negatively impacted the lives of residents. It's happening to me right now in my city: coworkers have reported their commute rising considerably over the past year.
So as the resident of a city who is happy with the way that it was, and is increasingly unhappy with the way it's becoming, what I'm wondering is: why should I not vote to block and prevent this growth? A lot of city politics talks as if growth is naturally a good thing that should always be pursued, but talk far less often of quality of life for residents. Growth often comes at the expense of current residents. (Gradual growth is healthy and necessary, but excess growth harms everyone.)
If discouraging high-density housing means higher housing prices, but buys me less congestion and a higher quality of life, then that seems like a good tradeoff to me as a resident. Otherwise, I get higher housing prices and more congestion and a worse quality of life. Cities should serve their current residents first, and prospective future immigrants second.
I suspect that the strategy that San Francisco residents are pursuing is a strategy designed specifically to make it expensive to live there, to discourage further immigration that they do not want.