What people have in the absence of government is not property, but merely possession. No more or less binding on anyone else than a dog with a bone.
You have to wonder if the framers talked about our actual natural rights in such disrespectful terms: "The saying there shall be no monopolies lessens the incitement to ingenuity, which is spurred on by the hope of a monopoly for a limited time, as of 14 years; but the benefit even of limited monopolies is too doubtful to be opposed to that of their general suppression."
Does this strike you as being even remotely analogous to the situation faced by the people who make television, movies, books, and music?
So what? The previous poster's point is that both forms of property are social contracts. All private property, physical or otherwise, are nothing but societal agreements, regardless of whether there is a written record or what point in history the agreement began.
We now live in a world where the machines needed to copy things are commonly owned by individuals. Copyright, having been designed to regulate industry, is massively out of date -- individuals do not have the resources needed to decide if they are abiding by copyright. Even the entertainment companies that cry about the importance of copyrights know this, which is why they keep pushing for DRM. No sane person actually believes that normal people are going to stop and think about whether or not they are obeying copyright laws; that is just not how people generally behave.
The truth is, in the 21st century copyright is nothing more than a red flag law that exists solely to protect obsolete industries.