Most of the land in my (Massachusetts) town is zoned for single-family homes. There are several identifiable square-mile or larger areas with nothing but homes plus maybe one school and one church. Maybe a gas station / Dunkin Donuts within fifteen-minute walking distance. That's no way to live.

I'd love to change it, with greater zoning diversity and particularly that which allows higher density, but there valid objections to doing it all at once. Roads would need to be upgraded and then maintained, at direct town expense, plus dealing with increased traffic. Ditto for water and sewer lines, minus the traffic issue. Electrical, gas, and communications are better in that they're not at town expense but worse in that more parties have to be involved (and they tend to cheap out even more than the town does). And then there's schools - the town's crown jewels and the main reason anyone lives here. They're excellent but already overcrowded. Work is under way to fix that, but we really can't afford to add even more stress to that system.

These are very real issues that I'm sensitive to, even though I also think there are other issues - especially racial and income diversity - that we must address in the longer term. These same issues recur many other places, I'm sure including the Bay Area. It has to be not only allowable but profitable for developers to do the actual building, or else they won't, and then the town needs property-tax revenue from each tranche before they begin the next. It's a very tricky dance, and I do not at all envy the people on zoning/planning boards trying to reconcile all these conflicting needs.