re:"Republican abandonment of our core urban areas is far more costly than any failed social experimentation"
IMO, the problem has little to do with Republican vs Democrat, and more to do the money. Have you considered that probably even now, it is cheaper, quicker and less risky to construct the same residential or commercial properties in the suburbs than in core urban areas? In addition, usually, at the edge, the cost of land, labor, permits, and even the cost of delivering building materials may be much cheaper in the suburbs than urban centers.
Also you need to take into account the needs and desires of people. Suburbs have probably always had less crime than city centers. People who live at the city's edge, also can have a degree of privacy, that people (except the very rich) in the urban centers can never have. Parents can let their children play in their own backyards, adding to a greater sense of security for their children.
The problems you site are actually old ones, that pre date the rise of the burbs, or redevelopment, or red lining.
"A 1952 (Philadelphia) city planning report noted that many older wards had been losing population since 1920 or even earlier." -2000 The Brookings Institution |