Modernists didn't have a problem with any particular style, per-se. It was the entire concept of applied ornamentation and designing a building to look a certain way and fit within a predefined mold that they took issue with. With all the WWII advances in technology and engineering standards, they felt a building should aesthetically reflect its function and materality: hence all the exposed concrete, no real order to the windows, blank walls, etc. They were unforgiving "machines for living/working/building", nothing more. It was a revolutionary concept.
Also remember, modernism took hold in the US after a pretty long period of economic and cultural stagnation. Almost an entire generation of architects were out of work, and doing little more than working for WPA programs, if they could even do that. There was little to no innovation, and art deco never evolved into something new, it just stopped.
After the roaring 20s, the depression and then war rations made EVERYTHING, including the relatively new art deco buildings look old, outdated, sad, and dreary. On top of that, the US was now this massive powerhouse capable of doing anything, so why shouldn't they reinvent the wheel. Ironically, many of the modernists saw their form as going back to the greeks and roman ideals: after all, the arches, columns, colonnades, and domes that we so admire were invented to be functional, not for aesthetics. They saw what they were doing as much more pure and true to these ideals than say, colonial revival, with it's applied wooden pilasters, etc.
This wasn't the first time this had happened. Art deco, arts and crafts, streamline moderne and such all came out of the outright HATRED architects and the public had for the excesses in ornamentation and garishness of the victorian era.
Of course, eventually and to the bane of the innovators of modernism, it eventually became a "style". So you had everyone and their mother putting drywall, homasote, and fake wood paneling over period detailing in their historic homes and offices, you had
this building on Market St in Brighton converted to
look like this, etc, etc. Keeping up with the Joneses, and all that.
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Anyway, back to our originally scheduled programming.
I wish they would repave Washington with something other than red brick. It looks so 1980s trying to look like the 1880s its sad. Not only that, but the red brick simply clashes with nearly every building on that street.