ARE WE TIRED of leftist infighting yet? The revolutionary fervor of two years ago is gradually dissipating into directionless, incessant debate over the correct path forward. Ours is not the first generation of radicals to be divided or silenced by liberal figureheads. A silver lining emerges, however, in the resurgent labor movement taking on Amazon and Starbucks, among other corporate and institutional giants. In recent years, a reawakening of worker militancy has rippled across the art world, resulting in widespread organizing efforts in the museum field.New York’s Museum of Modern Art—...