Actually Thomas Jefferson wrote a fair deal (no pun intended) on copyright and ultimately he was ambivalent as to it's benefits, but he certainly recognized that copyright's ultimate aim was to enrich the public domain and was not intended to give ownership to ideas.
"Stable ownership is the gift of social law, and is given late in the progress of society. It would be curious then, if an idea, the fugitive fermentation of an individual brain, could, of natural right, be claimed in exclusive and stable property. If nature has made any one thing less susceptible than all others of exclusive property, it is the action of the thinking power called an idea, which an individual may exclusively possess as long as he keeps it to himself; but the moment it is divulged, it forces itself into the possession of every one, and the receiver cannot dispossess himself of it. Its peculiar character, too, is that no one possesses the less, because every other possesses the whole of it. He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me. That ideas should freely spread from one to another over the globe, for the moral and mutual instruction of man, and improvement of his condition, seems to have been peculiarly and benevolently designed by nature, when she made them, like fire, expansible over all space, without lessening their density in any point, and like the air in which we breathe, move, and have our physical being, incapable of confinement or exclusive appropriation. Inventions then cannot, in nature, be a subject of property."
Also, copyright is a legal claim, so almost any argument about it will be rhetorical. (Rhetoricians and Sophists were basically the first lawyers) Copyright itself does not logically stem as a necessity of the conditions. With regard to rhetoric logos is one of the rhetorical appeals so even an argument based purely in logic can be rhetorical in nature.