You're describing a pleasant low population density situation which is a nice romantic fantasy a lot of people long for. I don't blame people for wanting that, but you must realize that it is the exact mentality that leads to suburban sprawl.

I think on aggregate, that is more expensive (financially and environmentally) than high density cities. Take all the infrastructure which needs to be built out for these small cities (roads, electric grid etc) which serve a very small number of people and now imagine if everyone lived like that and multiply that cost with building out this infrastructure for a many many small cities. Building 30 small idyllic villages instead of one hong Kong would end up having a larger environmental impact.