Because there need to be recognized limits so that people know if they are truly taking something from someone.I appreciate the point you have made, Raymond. It does seem that when contracts are involved, there is an 8th commandment violation. I still believe that in a context where there are no contracts, implied or otherwise, it is not stealing to copy someone's work. The operators of printing presses in early 16th century Germany were not guilty of violating the 8th commandment. When I want to obtain a work that has passed into the public domain, it is not my moral responsibility to track down the heirs of the author and negotiate the terms with which I will use their work. From what I understand, some here believe that copying is stealing regardless of the copyright or contractual issues. That is, ideas are inherently property of their creator. My question for them still stands. If this is true, why have IP terms? Why should a patent expire after twenty years?But when you buy a piece of software, there is a contract. It usually says something along the lines of "purchaser agrees to not make copies for distribution without permission from . . . ."This is actually a far better argument. Certainly one could protect their product by making the customer sign a contract. However, it generally isn't the practice to sign a contract when purchasing a book or CD, but maybe it would be in a world without copyright.
And almost every published book says "all rights reserved" and something to the effect that you may not make copies without permission.
Under the common law of contract, those are either express or implied contracts and are historically enforceable without a copyright scheme.
In both cases you buy something produced by another subject to the rules of use. So your proper choice is either to try to renegotiate the terms or to refuse to buy it. But once you buy it, you are morally bound to what you agreed to honor regarding the restrictions.
The exact same principle occurs in real property. It's called adverse possession. If after a period of time (bright line rule) no one else treats the property you are possessing like their property, you can have assurance from the law that it is not. The same is true of public domain laws.