Economists (witch doctors of dubious veracity in my opinion) and republicans are always harping on supply and demand to justify greed based pricing, but if we are to believe that low supply means high prices and high supply means low prices then you must argue that media piracy is just following the natural rules of capitalism.
It costs me nothing to store the latest crap movie with Julia Roberts on my disks and to share it. It costs others nothing to do the same. Therefore an infinite number of zero cost copies are possible. Supply and Demand says then that all copies should be free because the supply is endless like air or sunshine.