Don't forget the huge energy savings (heating/cooling, transportation, infrastructure) by having denser housing. It isn't just a measurement of "I can see trees," but all the daily human activities that have a reduced environmental impact in denser development. It's counter-intuitive, but rural areas that are "nearer to nature" are often worse for the environment.

There is probably a break-even point, I don't think everyone living in skyscrapers is ecologically ideal and I wouldn't want to live there anyway. But medium-density development with multi-unit (shared wall) buildings allows huge energy costs, while also making public transit more viable and providing a tax base that actually pays for its own infrastructure.