If there’s surplus land, why build something unwanted in someone’s backyard? I’m a suburban NIMBY homeowner and I feel like you’re actually making my argument without realizing it. I’m all for building new houses on unused land. Can you please just do it without ruining my neighborhood? Build nice new neighborhoods and make them as dense as you’d like, but don’t try to force density on older, established neighborhoods that can’t support it.
The empty land is not very valuable. Suburban homeowners are sitting on relatively valuable land, and it's valuable because of access to jobs and services.
In my personal experience, adding density to established neighborhoods improves those neighborhoods' character. Sometimes it gets those afraid of change to move out, improving it even more.
I'm actually curious - have you spent time in cities like Bern or Bilbao? I think urbanism's been a hard sell in the US because we don't really have a lot of great examples of it - New York's maybe the closest we've got to a European style city, but that's only in certain places and it's still a bit much. I was in Europe last year and I was surprised how calm some of the cities were - green, walkable, a lot of nice cafes and parks, good public transit, and it never really felt overwhelming the way that, say, Chicago or LA does. I grew up in the suburbs, and I felt like some of the smaller European cities delivered the suburban sales pitch better than a lot of places I've been in the US.
(Don't take this as an attack or critique - genuine curiosity.)