This is a very interesting and important issue. I believe that idea, not capital, is the defining factor of the free market (or capitalism, a misleading word in my opinion). If that is true, rules and agreements about intellectual properties are at least as important as those about physical properties.
I don't think there is a natural answer to 'what is fair'. It is arbitrary one way or the other. However, the goal must be to let the original creators sufficiently motivated and compensated, yet make it possible for people to make valuable works using the original. From this perspective, fair must be 'balancing'.