"As Commerce Secretary, he championed the Standard Zoning Enabling Act to address 'the moral and social issues that can only be solved by a new conception of city building,' " writes Rick Cole at Citiwire.net.
"In 1926, the Supreme Court upheld zoning to protect health and safety by 'excluding from residential areas the confusion and danger of fire, contagion and disorder which in greater or less degree attach to the location of store, shops and factories.' The quite sensible idea that people shouldn’t live next to steel mills was used to justify a system of 'zones' to isolate uses that had lived in harmony for centuries."
The end result? Neighborhoods where you can't walk anywhere. Notes Cole:
"Take any great place that people love to visit. You know, those lively tourist haunts from Nantucket to San Francisco. Or those red hot neighborhoods from Seattle’s Capital Hill to Miami Beach’s Art Deco district. Or those healthy downtowns from Portland, Oregon to Chicago, Illinois to Charleston, South Carolina. What do they all have in common?
The mix of uses that gives them life are presently outlawed by zoning in virtually every city and town in all 50 states."
I'm not sure if I'd go quite that far -- even Framingham recently allowed housing and retail again downtown -- but it is true that a large number of communities would not allow building patterns that were used to create great neighborhoods like Back Bay in Boston.