I found an article just now that I believe has the best explanation of the whole copyright/music/mp3 discussion going on. It takes answers from two different people, a law professor at Stanford and a representative from the RIAA. Two different people with two different reasonings. As you read on, you realize how the law professor usually speaks from hard evidence whereas the RIAA rep is speaking out of more emotion and some facts.
It’ll take about 30 minutes so sit back, relax and educate yourself!