The article doesn't mention tenement housing, and I'm pretty sure we have learned from those recent mistakes. Of course many places like Manhattan and Singapore have highly concentrated living arrangements without the problems of the old subsidized high rise housing. It is also not necessary for people to live in high rises to make public transit feasible. Zoning neighborhoods with new urbanism designs would make it possible. For example, driveways between streets could be eliminated as a concept in many areas, providing more concentration without overcrowding.