[keen]

Without copyright, I could take apart J.K Rowling's billion dollar Harry Potter empire by simply republishing and selling all the works myself, without compensation to Ms. Rowling.

No, you couldn't. Who would buy the works from you, when anyone can legally obtain them, free?

You might sell physical books containing the works, but then you're not selling (licenses to) the works themselves, just paper.

I imagine in a world without copyright, many people (though not most) would still 'pay' for works such as Harry Potter, through services like Amazon, iTunes, etc. Customers would demand that these services share revenue with authors, similar to the current model.

The point is, without copyright, no one would pay you for Harry Potter.