How do you argue against IP if you stand by that point anyways? If all forms are of either energy, matter, or both, and that energy and matter are equivalent, then intellect is as much of a property as anything else.
Simple. You own a piece of wood. You shape it into a chair and it stills belongs to you. The only thing you applied upon it is work.
I own my brain. I formulate a design with it. By your standards, it belongs to me.
Yes, you may claim that the "waves in your brain" or whatever are the result of your work done with your property (body) and therefore belongs to you. It's a weird claim but philosophically speaking it seems ok.
But if in the use of your property you cause consequences to my property, you have no right whatsoever to claim that my property now belongs to you.
For ex., if in the use of your legitimate creation you produce sound waves - which could still be considered yours - that hit
my brain or
my recorder, you're causing a (positive) externality to my property. Unless we had some sort of contract, that doesn't give you any right over what's mine.
The closest way you could voluntarily simulate IP is by using contracts. But for someone to be submitted to a contract he must have had agreed on it, and that's is the greatest problem with IP. If person A produces something and releases it to person B under some contractual rules, but B ignores such rules and passes such content to person C, person A has no recourse against C, only against B.
Calling a thief someone that downloads movies or music via p2p is plain calumny.