I've never really delved deeply into this kind of argument, but something that just popped into my head and made me wonder:

Why are we framing this as "intellectual property"? To put it another way, why are we framing this as "buying an intangible thing" rather than "paying a person for performing work"? Legal advice is an intangible thing, but we don't consider lawyers' opinions to be "intellectual property" once written down.