As Elia Kazan's defense of his decision to appear before the House Un-American Activities Committee and "name names," On the Waterfront is a deeply personal film about finding your priorities and convictions and having the courage to stand up for them. It is a heartfelt, moving piece of art, a gem of the cinema that contains one of the all-time great performances. It is at the same time misguided, despicable, and utterly classless. Such is the duality of art.
Some back-story: Kazan (as well as Schulberg, who wrote the script) briefly flirted with communism back when everyone flirted with communism, came to believe it to be an evil that needed to be defeated, testified to the committee as to his involvement and the involvement of people he worked with, and made this film to justify that decision. His testimony helped blacklist fellow filmmakers who had done little more than attend protest rallies and meetings, effectively ruining careers and lives. This action so disgusted the film community that he felt it necessary to defend his actions, and even managed to convince Brando (who was "sickened" by Kazan's testimony) to star in the film. Kazan went on to win Best Director, one of the film's 8 Oscars.
Since Kazan made no secret of his motives, it would be foolish, if not irresponsible, to ignore them when examining the film. Brando stars as Terry Malloy, a former prize fighter who helps mob leader Johnny Friendly (Lee J. Cobb) have his friend killed in order to prevent his testimony. With the help of a priest (Karl Malden) and his friend's sister (Eva Marie Saint), he comes to see the corruption and finally decides to testify himself after his own brother is killed. He successfully helps destroy Friendly and the union is able to get their rights back. Essentially, his testimony helps destroy evil men that are controlling lives, keeping people silent, and running the waterfront apart from any sort of lawfulness.