Why did critics connect On the Waterfront to Elia Kazan's HUAC testimony?

Critics frequently interpreted the 1954 film On the Waterfront as a metaphorical rationalization for director Elia Kazan and screenwriter Budd Schulberg’s decision to cooperate with the House Un-American Activities Committee (HUAC).12

In 1952, Kazan testified before HUAC and identified eight former colleagues as members of the Communist Party, a choice he made to avoid being blacklisted. Because the film’s protagonist, Terry Malloy, is a former boxer who chooses to testify against a corrupt, mob-controlled union, many historians and critics viewed the narrative as a symbolic defense of Kazan’s own act of "naming names" to authorities. By portraying the act of testifying as a moral imperative against corruption, the film mirrored the position Kazan took during his controversial testimony.231