What does "pounding sand" actually mean in this context though? Considering that the people in question are complaining because it's already happening to them? You can't just tell people to stop complaining about grievances.

People are free to complain. But the challenge is (at least in CA) is that the most minor complaints will hold up desperately needed housing projects.

Legitimate complaints (e.g. this will mess up traffic) are fine. "Neighborhood feel" complaints (e.g. this building is too tall, it doesn't fit the neighborhood character) should be met with "thanks for your feedback, but that's not a good enough reason".

Of course if there is widespread consensus among voters on how they want their city to be developed, fine. But right now, the current system allows a handful of very vocal opponents to development to derail new housing.

Agreed with you on all points. Unfortunately housing policy decisions are made at a very local level in the United States, and local politicians are accountable to a very small number of squeaky wheels. And they can't afford to ignore even a few highly pissed-off wealthy voters. So what you end up seeing is that the wealthier, whiter people living closer in have enough political power to successfully stop new development, and then the development that does happen occurs in farther out areas that are poorer and blacker/browner and have less political say, and that's when you get gentrification. Trust me when I say that East Bushwick is not anyone's first choice for erecting new luxury apartment buildings, it's just that SoHo and its ilk have successfully been fighting all new construction for decades running.

That's why doing housing/zoning policy at a much higher level, ideally statewide, would be much better. Japan has that (for their equivalent of states) and you don't see these distortionary effects. Then you'd see the development happening where it really truly does make the most sense, and as a side effect gentrification would be lessened because not as much new construction would be happening in farther out marginal neighborhoods because the demand would be satisfied closer in. Incidentally this also has positive benefits in lower commute times and less environmental impact.