That is, at least, debatable: If you compare the "cost" of P2P with the cost of conventional marketing - i.e. payola, which is now done at arms-length through promotional consultants - the cost to the creator of a work may work out to be similar. Whereas piracy is incontrovertably stealing.
Intellectual property laws were authorized by our Constitution for the purpose of making the public domain richer in the long term at the cost of allowing government to make laws making authors richer in the short term. Nowhere does it say anything about protecting record labels, publishers, etc.
P2P isn't a form of marketing. The vast majority of music that is being "shared" by the vast majority of P2P users is music that people only learned about because of the millions of dollars spent by the record labels in actually marketing it.
Sure, some of it's payola, but there are lot of other legitimate marketing activities (videos, advertising, press, retail distribution and support) that don't have that taint.
Intellectual property laws were authorized by our Constitution for the purpose of making the public domain richer in the long term at the cost of allowing government to make laws making authors richer in the short term. Nowhere does it say anything about protecting record labels, publishers, etc.
You're right, but the Constitution also gave the Congress the authority to pass laws that provided penalties for infringing those authors' rights in the short term too.