Okay, I'll try to do a better job of describing brutalism here than I did earlier when Simon asked me about it.

Brutalism comes from the general idea of alternative beauty. That is, it proposes that there can be beauty in that which is not refined or "finished". It proposes that the traces of creation can provide an intellectual and physical depth which rivals that provided by the finishing and detailing processes in more traditional design. It posits that the energy and exuberance of the "unfinished" work, hinting at any number of possible "final" forms provides a greater chance to find meaning and "hidden possibilities" within the work. There is also some influence of structuralism (exposure of the underlying) in brutalist architectural works.

To give an example from sculpture, one ideal of beauty when sculpting a body is to create a likeness which reflects only the subject, with no hint at how the sculpture came to be frozen in marble. Another is to quickly sculpt the parti sketch of the motion or idea being caught in soft clay, with hand prints and finger marks across the crude form. Does the "finished" design have a greater truth than the "brutal" one? Which is more evocative? Does the "forming" design give the viewer more room to interpret, or does the "perfect" design allow for greater subtlety and depth in the expression?

In architecture, the two extremes are the perfectly finished and detailed wall, where every surface is covered with a finishing material, then textured, then trimmed, and the brutalist structure where the marks of the concrete forms, and the tips of the rebars are the only decoration. Of course, the irony is that the brutalist surface, far from being a rough-and-ready surface of creation, is actually an extremely involved exercise in making the process of pouring concrete perfect (because in the end, it is a search for beauty, just an alternate form of beauty).

That is, while the surface *looks* rough, it is actually very expensive and requires a great deal of effort to produce. In effect, you're choosing to use concrete as a medium for achieving perfection, and to perfectly express the aesthetic of reinforced concrete requires a great deal more work than simply covering rough-poured concrete with plaster and paint.

By the way, there are non-reinforced-concrete expressions of brutalism, rough-sawn naturally-weathered lumber used as siding comes to mind (though it's not particularly structuralist in character). The physical complexity of the surface and the weathering process provide a depth that, properly handled, can be quite beautiful.