The Basel Miami Beach art fair was fun, writes Peter Schjeldahl; it is an example of the fairism that at the core of the current art market. But “one day, perhaps soon, someone in a convivial group of money guys at a bar will say, ‘I just got back from [name of art fair]. It was fantastic!’ Another will drawl, ‘You still into that?’ In the ensuing embarrassed silence, the bubble won’t burst; it will vanish.”