Zoning is a local government issue, not "some urban planner's" issue. If a community wants its own zoning to change, it can get its own zoning changed. What zoning prevents is someone from buying a piece of land in a community and foisting unwanted change onto it.
Edit:
As an addendum, I'm not referring to the "wrong kind" of people. I'm referring to too many people, or a facility with drastically different traffic patterns. Ignoring the "wrong kind" of people thing entirely, I could knock down a few suburban houses, and replace them with super-luxury furnished condo-townhowse-type things that would sell for the exact same as the surrounding neighborhood. This still would be a major change to the community, both in appearance and lifestyle.
There is a key asymmetry you're missing: people who already live in a community and people who want to live in a community are all stakeholders, but zoning boards are controlled by the former. People who want high-density housing in a neighborhood can't get on the board to change the zoning.
People who want to live in a community have their say in getting to pick the community in which they live. If you have already made the commitment to move (which comes at a pretty significant cost), you are in a much better position of being able to pick a place to live than if you were to make changes that impose on others a desire/need to move.
> People who want to live in a community have their say in getting to pick the community in which they live.
They don't have any power in the zoning boards. 100 people could want to buy and build high-density housing in Palo Alto, but 10 people who already own property there could defeat their intentions via the zoning board. There is no reason why the desires of the few should outweigh the demands of the market.
If you don't want to live around high rises, buy up the land around your house. You shouldn't get to achieve the same effect by preventing other land owners from developing their property as they see fit. The zoning laws that allow this sort of behavior just favor existing property owners over future property owners, and lead to globally non-sensical development choices.
But they have plenty of power in deciding which zoning board governs the land in which they plan to settle. The community regulations are part of choosing a community in which to reside. If they don't like the regulations that govern Palo Alto, they can suggest that Palo Alto change its regulations, and otherwise are perfectly free to settle in, well, anywhere but Palo Alto.
> If you don't want to live around high rises, buy up the land around your house
How does this scale? Here's a scenario: 100 people who don't want to live next to high rises but are perfectly fine living next to other single-family dwellings buy up 100 acres of land in LibertarianUtopiaLand and chop it up. They then sign a contract amongst themselves requiring community consent if any of them are going to drastically change their property, and require that any transfer of the land be accompanied by the same provision. Sounds quite familiar.
There's no national regulation saying that every community must use the same planning methods. It just so happens that there's a pretty good model for how the process works so implementing it requires less lawyers.
It is far worse than this. For the better part of the history of the world, basic arithmetic is 1 man and 1 woman produce > 2 kids. Those kids grow up and even if one of them is happy to live in their parents' home, the norm, hell, the EXPECTED norm in american society is that the adult children go out and make their own home. How are they supposed to do that when there are no homes available because all their neighbors sitting on the local board decided that you can't build any new homes? This kind of selfishness is infuriating and utterly indefensible. A system that allows such situations to occur is undemocratic and un-civil.
Edit: As an addendum, I'm not referring to the "wrong kind" of people. I'm referring to too many people, or a facility with drastically different traffic patterns. Ignoring the "wrong kind" of people thing entirely, I could knock down a few suburban houses, and replace them with super-luxury furnished condo-townhowse-type things that would sell for the exact same as the surrounding neighborhood. This still would be a major change to the community, both in appearance and lifestyle.