Kosmo Yagkoto, despite his use of the incorrect term, has rather done a good job on covering why monetary rationales for theft are flawed. Morally, one could also get into the concept that the morally wrong action of one entity (The gouging-level overpricing of a good, in advantage of a near-monopolistic status over the distribution of said good, as done by the RIAA with digital music media) does not necessarily automatically condone the morally wrong violation of copyright law, regardless of future intentions regarding purchases.
Futhermore, the illegal copying is wrong despite the fact that it does not deny the original owner the use of the music, because its further distribution could theoretically harm the original owner (Though irrelevant to the argument, facts have pointed to the opposite, actually; posted sales of digital media have increased since the founding of the first P2P networks). So long as harm to the holder of the original copyright is possible, and plausible (Let us be frank, if one assumes the worst of people, perfectly logical, it is easy to see the validity of the concept that P2P networks harm conventional sales), it is morally wrong as well as legally forbidden.
On the other hand, the side I personally favour, are those who say that regardless of the morally questionable nature of this, the RIAA should accept the improved sales of digital media and the illegal actions that have helped this, rather than irrationally press for the widescale enforcement of the laws, regardless of harm taken to themselves. The two articles by Janis Ian, a recording artist herself, are interesting reading on the topic, and include research and data on the topic from the time of writing (2002).
