Since the mid-nineties, contemporary art has been booming like never before. There is more of everything--more artists, more collectors, more galleries, more art fairs, more museums, more biennials, more interest, more industry, more pop, more hype. Some art professionals feel prompted by all this to reach for the revolvers of cultural pessimism: Mass Stupidity Is Killing Great Art Others--often the same people a short while later--defect with...