> In the case of both real and intellectual "property", there is a resource from which limited value can be extracted. There are a limited number of cows that can graze in a given number of acres, there is a limited amount of money that can be made by selling a particular molecule as a drug, and there is a limited number of tickets that can be sold during opening weekend of a film.
Land has scarcity; not everyone can use it at once. You've argued that the same thing applies to works currently controlled by copyright, but I (and many other people) fundamentally disagree. Movie tickets have scarcity because not everyone fits in the theater at once; just look at the lines outside theaters on opening night of a popular film. However, the film itself has no scarcity; that doesn't represent a moral statement, just a statement of reality.
That might mean that people making films have to find other ways to extract value, but as a culture that falls under "not our problem". For a film people want to see, clearly the existence of the film has value, and people have found ways to make that support the film; just look at things like Kickstarter for one example, which would work just fine without copyright. (They'll probably work far better once they become a necessity; right now they have to compete with the effectively subsidized development of works controlled by copyright.)
Also, the ability to interactively change our culture represents a feature, not a bug. (Among many other things, see https://en.wikipedia.org/wiki/Remix_culture .) We deal with media we find distasteful by giving a collective "ewww" and moving on. That doesn't invalidate the huge value of having a rich public domain. (And in the case of Disney and numerous others, note that most of their movies couldn't exist without a rich public domain for them to have drawn from.)
> So it seems to me that opposition to intellectual property can't come from "legitimacy," unless we also consider ownership of real estate to be illegitimate. That would be a sad state of affairs, because I think the human race would be worse off without the idea of land deeds.
"Understatement" doesn't quite cover the implications of not respecting the exclusivity of property. But no, your premise doesn't hold; no natural scarcity exists for copyright and patents as presumed by the loaded phrase "intellectual property", the way it does for real estate.
Classic sci-fi thought experiment: if someone invented the replicator tomorrow, what else suddenly has no natural scarcity? Real estate would rapidly become the only component of the physical world with scarcity; apart from that, only services would have value.
> Edit: RF spectrum is another example, I suppose -- there's a limited amount of value to extract (only so many channels), and there are conflicting uses that create different kinds of value (which applications to run on which frequencies with which propagation characteristics.) And the policy tradeoffs in spectrum "property" seem to be different again from those in real or intellectual property. For one thing, there's the rapid advance of technology, and the possibility of spread spectrum.
RF spectrum absolutely does have scarcity, albeit somewhat flexible scarcity since we continuously find new ways to pack more into less. I don't think we currently handle spectrum regulation in the most efficient way (auctions don't necessarily seem like the right approach), but RF spectrum does at least have a legitimate claim as a limited resource that needs some kind of special handling. That said, the value of special-purpose RF protocols has gone down significantly, compared to just finding ways to connect devices to the Internet.