[JoeJonathan]

LA was zoned for ~10 million as recently as 1960. While I think you're right that the problem is probably intractable—who would want to give up their house for an apartment, unless maybe a dense, walkable area appeared overnight?—I wonder if there are legislative solutions, like rolling back Prop 13 (which will probably never happen).

[strangesongs]

But people don't have to give up single family homes to create density -- we just need to build more of everything else, wherever we can, to increase housing.

No one is coming for existing single-family homes -- they can peacefully co-exist alongside properties that house 5x the amount of people.