One of the projects that almost always comes up as one of modernisms greatest failures is Boston's Government Center. The Project for Public Spaces actually rates it as the worst square in the world. The centerpiece is the weird-ass-upside-down-concrete-spaceship that is Boston City Hall. I've been hearing a lot of people saying lately that they should just tear the whole thing down.
Now, the City Hall fails in a lot of ways, it sits on stilts, so it's hard to access, It blocks the view of Fanueil Hall from Scollay Square, but most peoples problems with it are on aesthetic grounds. I've been reading the book Lost Twin Cities, which is great by the way, and I've been struck by how many beautiful Victorian buildings were torn down in the 40's and 50's on aesthetic grounds. At the time, people saw it as gaudy and ugly. So here is my new thesis on architecture: people will (almost) always see the dominant style the proceeded the current dominant style as being ugly and unworthy of protection. Preservationists (and us) should therefore do everything they can to protect more current building types until such a time as they can be correctly judged, even if that means working hard to save some awful ugly buildings.
The old Gutherie Theater in Minneapolis is another example of a modernist building that people see no use in saving. My father in law once said he didn't see the point, it's just another glass and steel building, which might be the case, the thing is, people aren't building glass and steel buildings in that style anymore. It won't be replaced if you knock it down, and in 50 years, when people appreciate modernist architecture again, they will judge us by our failure to save these sorts of buildings.