It was a heroic and revolutionary age. The old order would be swept aside. Socially, the pig culture of materialism and acquisition would yield to flower children, pacifism and drugs --at the same time that architecturally the pig culture itself swept aside the last vestiges of traditional urbanism and construction in favor of slick, fresh, revolutionary, international Modernism. Leading the charge were Mies with his prescient Seagram Building, SOM (Chase Manhattan), Eero Saarinen (CBS, TWA), Louis Kahn (Yale Art Gallery), and in Boston, Kallmann and McKinnell (City Hall and Garage), Paul Rudolph (Hurley Building), Walter Gropius (JFK Bldg.) and Jose Lluis Sert (Holyoke Center, Peabody Terrace, B.U.).
Cheerleaders and facilitators for the new age of Urban Renewal were Robert Moses (New York) and Ed Logue (Boston). These worthies and their business and political allies unleashed an orgy of destruction that claimed the West End in Boston, almost Greenwich Village and SoHo (Jane Jacobs saved these by defeating Moses), and various Beaux-Arts monuments as chronicled here:
http://www.archboston.org/community/showthread.php?t=937&page=42.
Ironically, we're at this moment contemplating doing the exact same thing to the artistic monuments that resulted --and using the identical arguments: Boston City Hall and the buildings of Rudolph and Sert are declared to be ugly, obsolete, dirty and sitting on valuable land primed for more progressive development.
Who says history doesn't repeat itself? In architecture, the cycle's about 40-45 years; that's how long it takes for a style once thought to be cutting edge to descend to its popular nadir. If it can survive the ensuing quarter-century-or-so of being hated, it can expect to be nicely spiffed up for immortality. If City Hall survives the next twenty years, it'll be with us in the year 2200 (don't know about us, though).