“American Son”, a gripping new play on Broadway, is piercingly of the moment, thunderously bleak, written in all caps, and indulgently depressing.  Kerry Washington gives a devastating performance as a black mother living the nightmare of her son interacting with the police, but blunt writing provides shorthanded dialogue and characterizations that are unrealistic and convenient—tooled for the sake of advancing arguments, and provoking the audience, rather effectively serving a coherent social or political mission.