[millimeterman]

I think humans have demonstrated time and time again that densely constructed cities are a desirable place to live. Are there some people that would leave if these cities started loosening zoning and allowing dense construction? Sure - not everyone wants to live in a big city. But I would argue that the net change in population would still be massively positive.

Besides, why should existing homeowners get a monopoly on deciding what kind of city Santa Cruz should be? If there is a desire for dense housing, then dense housing will get filled. If you're right that people moving to these cities want suburbia then one would expect new multi-story apartments to go empty. But that's clearly not what happens.