Why zoning

While we're still stuck with zoning (and it's associated problems), its good to understanding where zoning comes from: the peculiar conditions of post-war America. The way is done, it's 1945, it's a war economy, with a combination of price controls, wage caps, rationing and subsidies in place. The wage labor market is tight (despite having drawn huge numbers of previously non-wage female workers into formal employment).

But at the same time, there is a huge amount of the labor pool is still across the ocean as an occupying force that is about to come home, and a complete horror of unemployment that is going to result when all those guys come home.

There has only been a tiny amount of new construction in almost a generation--1930-1945. The whole built environment is run-down and functionally obsolete. While not everywhere is a slum, everywhere is run-down. And there are plenty of actual 'Hoover-ville' shanty towns.

So there is a clear need to build a massive amount of housing. The Federal government has been playing  footsie with social housing (Greenbelt, etc), following the lead of what major cities were doing pre-war, and what it had to do for the dependents of the enlisted population during the war.

It's the form of American post-war housing that's notable--America went hard for detached single family housing. And as near as I can tell, it's purely due to the "No man who owns his own home can be a communist". That aside, why the strict segregation of uses? Lots of places have zoning without it (Japan most notably). 

The legality of zoning was in question for a long time. Euclid vs. Ambler is the court case that establishes the legality of zoning, says it's ok to segregate uses.

Anyway, intent of zoning is 'hygienest'. An urge to separate like from unlike. Because all the existing development seemed unclean--too much overcrowding. 

But the functionally obsolete matters. There had been a lot of technological change from 1928-45, no small amount of it driven by the needs of the war itself. Stoves and furnaces are the things that come to my mind, but bathrooms (indoor plumbing with a porcelain throne) also a shift for a lot of America. (Surreal, but many tenement buildings had only a single bathroom per floor).  'Cold water flats', with no water heaters in the building (let alone the units) also a thing.