Shylock is made to be the villain in the play, but reading or viewing it from a 21st century mind-frame makes him look like the victim for many reasons. One reason that Shylock can be pitied is because of Antonio's personality. Antonio is a Christian merchant who has treated Shylock with great discrimination in public by spitting on him and talking badly about him. Shylock's nature and as a Jew is one that seeks to defend himself when the opportunity presents itself. Antonio represents the thoughts and feelings of Christians of Shakespeare's time whereas Shylock represents those of Jews. Between these two characters part of western culture can be defined and explained; the question "what happens when two completely opposite beliefs come into conflict" is examined and partially answered during, and at the end of, the trial.
Bassanio and Portia are opposites, too. Not only are they gender opposites (obviously) but they are financial and intellectual opposites, too. Portia is brilliant, wise, and witty. That is not to say that Bassanio is an idiot or a clown, but he doesn't seem to be very good with managing money or clearly thinking things through before executing them. Portia, on the other hand, manages her late father's great estate and can decipher the law better than any of those men put together during the trial. Where Bassanio is a consumer, Portia is a creator and a problem solver.