SarahC:

There is a connection in historical fact between modern art and architecture and social utopianism. It does seem to cut across the grain of my own ideas.

Modernism in architecture is fundamentally an expression of utopianism. Constructing buildings, public spaces, and interiors that will be pleasant and attractive for people has been a well understood problem for thousands of years. A modernist, however, sees sticking to this body of well-established knowledge and experience as insufficiently idealistic and sophisticated, and strives for more exalted achievements that he believes his brave novelty will enable -- in the most extreme form, even seeing himself as a man of science proudly sweeping away the old superstitions.

Such idealistic hubris, of course, backfires in practice. This is best seen when looking at the artistic sketches of planned modernist projects that show people happily hanging out in the future modernist ambient, and then comparing them with the resulting bleak, despair-inducing, deserted spaces. (It is remarkable how not a single traditional form of architecture from anywhere in the world, to my knowledge, has ever created anything resembling the specifically modernist forms of ugliness and inhumane sterility. It takes the modern utopian thinking to discard common sense to the point where one starts to do such things.)

This example effectively answers your recent question what I have against utopianism. The utopianist ignores the limitations imposed by reality when embarking on his utopian projects, and when this backfires, others also have to live with the consequences. Some people see this clearly in advance, and understandably get nervous and aggravated.