Who should decide how dense an area is if not the residents of that area. Let's say I'm 25, and looking to buy a home to raise a family in for the next 20+ years. I get to choose if I want to live in a dense city, a sprawling suburb, etc within my budget. After choosing the density I prefer, why should outsiders be able to dictate what's best for a community and change it from what the residents chose to buy in to and how they desire to see it continue?
And yet why should my neighbors have any authority over what I do with my property? Who should decide how dense an area is? Well, if it's my property, then the answer is me. Unless I'm creating a nuisance, it's no one else's business.
Note that I don't actually believe that -- I am actually in favor of really good urban planning. But it seems to me we have the worst of both worlds here. People seem to think that they should have the right to control what their neighbors do and the government should protect their own property interests by ensuring that the neighbors do only those things that they view as positive. And yet the minute you talk about intentional planning efforts, those same people will all be whining about the government interfering with their property rights. You really can't have it both ways.
IMO the biggest problem with most zoning is that is largely solidifies a long history of redlining. Many years ago, you could directly say "no ______ allowed" in a property deed or zoning regulation. Once those were outlawed, we shifted to the "unstated but understood" rules about "those" people. And now we're all so sophisticated that we've managed to shift the whole argument to one about socioeconomic status. And yet while those original directly discriminatory rules are no longer on the books, the system of neighborhoods that were developed based on those rules remains the same and in fact has now been codified into pre-existing property rights.
I think any zoning should be done on a state-wide basis, with local planning experts representing each area. Right now, there is a huge disincentive to change the status quo, because if your local council rep votes for more dense zoning, they're going to be out on their ears the next election, no questions asked. So there is no incentive to look beyond the status quo. Meanwhile, various parts of the state tend to be growing rapidly, and yet the state has no way to actually plan to absorb that growth in a thoughtful manner that deals with things like traffic and stormwater runoff and mass transit and all that.
One local example: near me is a small old mill town, located at the bottom of a valley. Over the past 30 years, many developments have sprung up in the surrounding hills (some in the same county, some in an adjoining county). As a result, the town has experienced two major floods over the past 10 years, people died, and the county has now condemned/demolished some of the town and is having to completely rework the river system as it goes through the town. Every single one of those new developments was constructed completely in compliance with the applicable environmental and zoning laws. Every single development replaced some forests/fields with some acres of impenetrable concrete. Individually, each decision was meaningless and even sensible, given the demand for local schools. And yet the combined effects of each of these individual decisions has had very significant impacts on the people who live downhill -- and left the county and state holding the bag to fix it.