Certainly the ones who oppose it are wealthy elitists.
On the other hand, everything I have ever heard about this idea of "filling in" seems like homeowners who want to rent out their alley without having to conform new-built residences to code so they can maximize $$$$$.
Do other cities have this "movement"?
I have been interested in the insurers that are pulling out of Florida & California as the climate disaster risks become to high for this reason. Once home insurance isn't available housing is no longer a great investment, new buyers can't get mortgages, home sale price seems like it would have to drop in response which I guess causes a lot of current mortgages to go weird. And as a bonus both states are on "opposite sides" of the political spectrum and will be just comically unable or unwilling to deal with the problem but presumably in different flavors.
This is going to be shitty for people but seems like it is better than the status quo existing in perpetuity. It will be like having a glimpse a few years into the future for most other states.
In that scenario, housing only goes down in value because the underlying conditions make the area unlivable, leading to mass migration elsewhere (which we're already seeing in some parts of the world) and a commensurate drop in economic activity in the area. It doesn't make housing more affordable, it just makes it less desirable, plus it puts upward pressure on housing markets that receive climate migrants. It will effectively make housing less affordable because it takes certain geographies out of the equation. Not only are they not making more land, but there will start being land that becomes effectively uninhabitable. The status quo has already priced all of this in. There's no condition where housing becomes more affordable without meaningful changes to how housing is owned and distributed.
But, to be less doomer about it, there is nothing inherently blocking the creation of better ways to do housing. The market won't provide affordability, but that doesn't mean that housing can't be affordable. It's not a problem that needs to be handled all at once at all levels, the problem can be broken down and solved in different ways in different places. There are plenty of levers to pull to solve the problem, and the pressure to start pulling those levers is only going to grow. It's a good area for organizing, and for finding people who are already radicalized, it's just that the current status quo is shitty and isn't going to get better without changes.