I wanted to address this earlier point as well. I think people have moved beyond the 20th century notion that "the solution to pollution is dilution". Airborne pollution in particular is no longer localized - it transcends individual cities, and blankets entire regions. And a lot of it comes from traffic. If you move a few million people out of New York and scatter them into some kind of vast rural diaspora, they're all going to have to start driving everywhere, and air quality all across the United States will get worse.