But why does the high density housing have to be where the SFH are? Why does it need to share the parking, facilities, retail, roads, schools, etc. of something that was built and has been maintained and evolved for 50-100 years? Why not build the high density with it's own transit, roads, malls, parks, schools etc?

This is how it's done in the rest of the world, certainly Korea, Japan, and China. I see this in England and France as well. They develop a high density area with new facilities that can grow and evolve for how people want to live there, rather than mowing down houses (in communities of color) or plopping 5-7 story apartments without parking or parks right next to single story SFH, as developers like to do in the US.

I assume it's because it's more profitable for the developers. They don't have to build anything, but the part they can immediately sell, and they ride on the value of the neighborhood created by the people who already live there. I think some infill near commercial districts or malls also faces much less "NIMBY" criticism.

To give a more personal example: I like the location and view of where you live. I like the plants you water, and you keep the house looking clean. I want to just build another large room on top of your house, where me and a bunch of friends will live. We'll just share the stairs, hallways, and front door, and of course our share of the water and electric bill. We probably won't be too loud most nights, and usually when friends come over they won't use your bathroom or take anything from your rooms, or at least we'll ask them not to. Sorry about the construction noise while we do it, and just think you'll get to meet so many new people! Sorry that the part of your house you still own will be worth less than your neighbors when we're done, but that's the price you need to pay for living in a nice place and keeping it up.

The argument that SFH infrastructure repair is subsidized by new building is a much better one. Of course that was true of the tax increases and subsidy of the original town, when the SFH were built as well.

Absolutely, but this is just the opposite logical extension, corollary to "if we allow infinite development, there will only be a dystopia of super-high-density living everywhere".

Both things are bad, and we must "prioritize" a balance, not one or the other. It's perfectly possible to build inward/upward in some places, and outward in other places. It's perfectly possible to build affordable/high-density housing without ruining existing areas. It's perfectly possible to accept that some places are highly desirable because an infinite number of people can not live there - that certain amounts (high amounts) of development defeat the entire point by removing the desirability of those locations. We can strike a reasonable balance between allowing developers to do whatever they want without regard for infrastructure or community, vs, on the other end, not allowing any new construction in already-populated areas.

We can expand existing desirable areas reasonably, while also building new desirable areas, but that's difficult because it requires time and investment, and in the meantime it's not as "desirable" as people would like. The simple fact is that people are reproducing within and migrating into desirable areas at a rate that is not compatible with keeping those areas desirable, and developers are leveraging this conflict to pretend they can't build anywhere else, hence the crisis.

More shortly: You're understating the importance of quality of life (the concept of "home" is one of the most important things in the history of humanity), and implying a false conflict that we can't both have both quality of life and more development.

If all the things you describe came to fruition, the current residents will have to live with the consequences of their decisions and suffer a lower quality of life (which they don't want to do), and the problem would resolve itself.

Or in reality, desirable locations remain desirable, and the current residents who had a hand in making it desirable have a right to prevent a reduction of their quality of life for the benefit of people who would prefer to live there but are unable to successfully compete with others in the housing market.

You're confusing amount of money with amount of people.

Financial investor mindset is a real and dramatic example, but a minority in the set of reasons that individual people care about the community they worked so hard to live in.

No need to be obnoxious. Just say that your opinion/experience is different.

It seems natural to me that the majority of emotions regarding one's home and community are in regards to the idea of home and community, rather than their monetary value, since that's the obvious human perspective. And of course you can care about both things at once, which maybe you assumed I was omitting? I only said the the majority of people care about their home/community, and implied that I believe it's the stronger emotion, not that the majority of people do not also care about the investment (which does materially affect their actual life, as opposed to the more common image of a wealthy "investor").

I could be wrong. It's a sentiment, so it's not something easily measured (unless you fall for the trap of over-interpreting statistics, which is common in an engineering-minded folks).

Development raises land value. That's the entire reason it's done, after all. Look at the cost of land in Manhattan vs suburban Atlanta. In the supply-choked cities in the US, development isn't gonna tank the wealth of land-owners, quite the opposite. There are exceptions, but they're "this is the largest available plot in Beverly Hills"-style outliers.

What people want, even in those denser supply-choked cities, is basically just stability. "I don't want to be forced out because a bunch of rich people move in next door, and I don't want it it turn into something dramatically different experience-wise than what I bought."

If everyone in those areas just wanted to maximize the financial side they'd be looking to flip their single family home for a fourplex and put the profit into another, etc etc.

"We don't want this to turn into Manhattan" is NOT what anyone owning land in a maybe-could-turn-into-Manhattan place if they were just interested in the money.

(That's less viable in the middle-of-the-country suburbs because the "increased land value" of the old empty pasture next door could still result in lower land value for your on-the-suburban-fringe neighborhood, if there's high amounts of empty land and more new identical suburbs popping up. But that's not where the problem is most acute, anyway!)