I'm not sure I buy this argument. 

Allow me to play devil's advocate, as I'm not sure I fully agree with the position I'm about to present.

If I never see your writing, there is no way for me to copy it. In order to copy it I must first see it. If you were to make your writing available only under a conditional contract of sale (copyright) that states the writing is not to be shared with anyone else, and that contract of sale is made known prior to any exchange of said writing, then the only people that ever see this writing and will be "forcefully" bound to the contractual agreement are those that agree with it. No one is forced to not copy it if they don't buy it, and by buying they enter into a contract of sale. In other words, copyright does not try to remove things from the public domain, it tries to prevent them from entering into the public domain in the first place by restricting the sharing of those things to a community of people who respect the conditions of it being shared. 

The only cases where I feel like your argument could hold is when I am forced to read or listen to your work due to public broadcasting. However, except for perhaps some severe fascist states, it rarely happens that people are forcefully exposed to media in the first place that they are then denied the right to copy it against their will.

Your thinking is in the right direction. Indeed, if you are given a book under contract, then you have to abide by the contract. But let's say you decided to break the agreement and copied the book on the Internet or gave it to your friends. All those people made no contract with the author and thus they cannot be and should not be bound by the contract. What copyright does is bind third parties, which never agreed to the contract.

There are other cases. Public broadcasting is one. You turn on your TV and see Harry Potter. You were not presented with any contract. Why should you be bound by any conditions? If the author of Harry Potter wanted to distribute her book only under contract obligations, she should not have let it broadcast on TV.
The other case is the one I mentioned - someone breaking a contract.
There are other options, like accidents. You leave a book on a bench. Unless the book itself contains a full blown contract in it, there is no way for Joe who finds the book to know. In fact, even if the contract is in the book, Joe did not sign it.

Additionally, some things are just out there. You invent something. The other person sees it. He has no contract with you. Why should he restrict actions with his own body and his own property? What legitimate reason is there to not act on a new knowledge you have?

Finally, if each time you enter a store and decide to buy a DVD, you were explicitly told that you will not simply be able to share copies, but that you should agree to not use the knowledge you gain from the DVD and act as if you have no such knowledge, I am not sure most people would agree.

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Staat heißt das kälteste aller kalten Ungeheuer.  Kalt lügt es auch;
und diese Lüge kriecht aus seinem Munde: 'Ich, der Staat, bin das Volk.'
                                                - [Friedrich Nietzsche]