FOUR DECADES IN, Paul McCarthy’s art might easily be considered repetitious, overblown, big-budget, anxiously relentless. Is that his problem, or is it America’s? The question is worth asking, if only because McCarthy, like Warhol before him, totes a get-out-of-critique-free card: His art is a mirror to his homeland’s times, at best the convex type that allows a view around blind bends—though should it descend into costly gibbering spectacle, there are always enough analogues and portents in the parent culture to still render it defensible. Even so, there are inevitably qualitative variations