In most of Europe, the majority of the middle-class lives in housing where at least one wall is shared with a neighbour (whether it be apartments, semi-detached or terraced houses). For that matter, most middle-class New Yorkers live in apartments or other high density housing, and seem to survive.

Just replying about 'balconies' - I //hate// them as sources of noisy neighbors and neighbors that smoke and thus ruin the air around where I live.

I also dislike how MDU exhausts, particularly the laundry exhausts, are not sent out a scrubbed (E.G. water filtration) negative draw system to remove the fine particulates. I have never in my life even seen an MDU with such a setup, let alone filtered air ingress delivered to each unit.