Hi, everyone, it's Hannah. First of all, I really want to agree with Jill--it is a frightening thought. If the one man had not defied the status quo, the jury would have come to a hasty and potentially incorrect verdict which would have sent an 18 year old man to the electric chair. Just to answer one of Mr. Perkins questions, I don't believe that prejudice is ever helpful in the court of law (ideally, of course, justice is blind, but we see that this isn't always the case). What is helpful is background knowledge, preferably objective, although personal experience can come in handy as long as it does not infringe upon the bearer's ability to make rational decisions.
In this case, prejudice was not a good way of knowing the young man's guilt because it was simple, boorish prejudice: He must be guilty because he is from the slums, has lived around violence, and so must be prone to violence himself (remember the Broken Chain???). Once the jurymen heard this one tidbit of information, their minds were closed to anything else which may have swayed the case.
Just to add a bit more thought to the subject, I want to quickly bring up some information about human emotion. There is a part of the brain called the Limbric system, which is responsible for emotions. The part of the brain responsible for rational thought is located in the frontal lobes (the Limbric system is near the center). When something happens to a person, the 'knowledge' of this enters into the brain around the medulla oblongata. The signals have to literally pass through the brain to reach the frontal lobes where they can then be analyzed rationally. That means that in most conscious circumstances, the signals have to pass through the Limbric System (think of if someone accidentally bumps you in the hall. Within milliseconds, you think: 1. ow 2. why the heck did they do that?! jerk. and maybe 3. it wasn't personal; they are probably running to get to class on time). What happened in this movie is that only one of the jurors was able to think rationally about the verdict; everyone else was caught up in emotions and prejudices. They were literally rushing their thought process and one was actually genuinely more concerned about a baseball game than a life. As the movie climaxed, more and more jurors allowed their thought process to move away from the Limbric System and into the rational part of the brain. There were only a couple of people still stuck in the Limbric system when we ended, and they looked and acted like fools.