The bankers themselves are played by Tony Shalhoub (Monk, Wings), Evan Handler (Californication, Sex and the City), and Bill Pullman (Torchwood, Independence Day), among others. They are not really the blatant villains, as one might expect. While the companies they represent do take a large portion of the blame for what they have done, the men who run them generally come across as hard workers, willing to make sacrifices. They want to save their companies, but they are also willing to make a move that benefits the system as a whole, which in a roundabout way, does save their companies.
That doesn't mean the bankers are heroes, by any stretch of the imagination. Obviously, it is because of them and their companies that the chain reaction of disaster begins. They also pocket American tax payer bailout money, which they will only take without strings, and continue to pay out huge bonuses. The public is justified in their anger at them. But because the film is made up mainly of closed door meetings of individuals, these things are sometimes downplayed, making them seem like decent guys. Hallway rants by Paulson allude to another side of the story.
Actually, the people who come off the worst in the film are James Woods (Shark), as the head of Lehman who hesitates to try to make more money, not realizing it's too late to save the bank, and Congress, especially John McCain and the GOP. They are all slow to act, and work against what Paulson insists is necessary. It's a battle to get them to do what has to be done, and because of them, the whole system almost goes belly up several times.
Also looking bad are the British, who have a chance to help, but sabotage a good deal that may have saved the system at the last minute. Furthermore, they begin to freeze credit after Lehman's collapse, worsening the situation. While Europe will be deeply hurt by what happens on Wall Street, they show an unwillingness to believe that America can take them down, too.