“ONCE YOU could tell a lot about a community by its church,” the American architect Philip Johnson, himself a great museum designer, has written. “It was the place the city took pride in. Now it is the cultural center, the museum as monument.” A cultural center could be expected to come under attack in a culture whose center cannot hold.  Today the traditional conception of the museum as a dignified location for the display of artistic masterpieces is threatened both by ideological criticism from the left and, perhaps, by the market-driven substitution of entertainment for enlightenment.  Ironically, neither of these challenges to the institution is as radical in its implications as a long-neglected critique from the philosophical right that calls into question not only the idea of the art museum, but the very idea of art.