You drive down housing costs by building more housing, full stop. Housing is expensive because the supply is extremely limited, and the supply is limited because it's too hard to actually build housing, because governments and NIMBYs seemingly don't want more housing.
There is tons of cheap, prefab housing available, they're called trailer parks. They're everywhere except where you want to be. The anti-NIMBY argument basically boils down to "If I can't have that house, no one should have it. Let's invoke the unfairness of life and have it torn down, or else build a vertical trailer park next to it."
The YIMBY crowd basically boils down to "do whatever you want, I don't care, just don't stop me doing what I want". More basically, "government regulation bad, capitalism good". which happens to be one of the Republican party's main platform points (in theory, but only when it suits their own goals). The YIMBY crowd doesn't want to tear down your house, it wants to let YOU tear down your house and build something more profitable in its place.
Activists recently prevailed on my city's government to rewrite the zoning ordinance, making my block of single family homes eligible to be torn down and turned into 4-plexes. I personally don't have a huge problem with it - from a libertarian point of view - because in theory, that means exactly what you said. I can sell my property for more money or develop it and make more from it. The aspect of it that irritates me is that those weren't the conditions under which I bought the house, and the reasoning behind the change was a foolish sop toward social justice, and clearly comes from a place of sheer hatred born of jealousy toward anyone living in a single family dwelling. I wouldn't have bought the house to live in if I'd known that ten years later it would be surrounded by apartment buildings. And so that plus the castigation of people trying to maintain their space as "NIMBY" leaves me mainly with the attitude that they can have it, I'll take the profit and move somewhere they can't afford and have less leverage to screw up.
Again, trailer parks have been a thing for 70 years now. The innovation here has been rewriting zoning rules without actually rezoning, to bring the trailer park to people who can afford to live somewhere better. The funny thing about class warfare, though, is that people take their lack of class with them and end up making slums wherever they go, and other people manage to make a buck and stay ahead of them.
The only constant in life is change.
Or as certain fictional character said, "Nothing is a line. Everything everywhere is always moving forever. Get used to it."
Buying a piece of land doesn't entitle us to control what happens on neighboring pieces of land.
My parents house used to be surrounded by farms and woods, now it's surrounded by homes.
100 years ago 5 story brownstones in NYC were surrounded by other brownstones, then by mid-rises, and now by high-rises.
The vacant lot next to me is now going to be developed into a house. If I wanted it vacant, I should have bought it and carried the RE tax indefinitely.
No one is banning single family homes. We are just trying to reconcile that the main cost lever is density, and in a country with growing population, mostly crowding into a few metropolitan areas.. if you want the next generation to be able to afford a place to live, we can't leave the real estate market ossified.
This is an attempt to change some laws set by the previous generation that restricts your right to develop your land, and freezes the housing market as it is, constraining supply.
If the state was literally banning the construction of single family homes, or taking yours away with eminent domain, you'd have more of a leg to stand on.
> The aspect of it that irritates me is that those weren't the conditions under which I bought the house
There were no conditions that the surrounding properties wouldn't change over time. You might have thought there were, but it was an illusion. If you want to control your neighborhood, buy it for yourself.
> the reasoning behind the change was a foolish sop toward social justice, and clearly comes from a place of sheer hatred born of jealousy toward anyone living in a single family dwelling.
This is ridiculous. The reason behind the change was likely because residents of your city want cheaper housing, and your government is trying to make that happen. Most Americans grew up in single family homes, but that doesn't necessarily mean they want to keep living there themselves, and any animosity towards single family homes is because these people are forced to live there because nothing else is available in their city, and they would rather spend their money on something else rather than a single family home.
Your suggestion that denser housing options like low-rise (plexes), midrise, or even highrise are "slums" is patently false.
