In an affidavit supporting a lawsuit against a new novel related to J.D. Salinger's Catcher in the Rye (New York Times, 6/17/09), Salinger's literary agent makes a statement that encapsulates a common misunderstanding of what copyright is for. Referring to Salinger, the agent said, "He feels strongly that he wants his fiction and his characters to remain intact as he wrote them."
Salinger may feel that as strongly as he likes, but the purpose of copyright is not to allow creators to protect the ideas they create from being used by other creators. The point is to give creators a period of exclusive right to publish their works in order to give them an incentive to create those works in the first place–as the Constitution says, "to promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries." A key word here is "limited."
When Salinger first published Catcher in the Rye, in 1951, that period was 28 years, which could be extended at the creator's option another 28–for a total of 56. Evidently, the prospect of making money from his novel until 2007 was sufficient to get him to write the thing. And that's all the copyright law is supposed to do.
The fact that Congress has stretched the idea of "limited" so far–the latest revision extends copyright to the life of the author plus 70 years–does foster the misperception that ideas naturally belong to their creators, and they alone can decide what can and can't be done with them. But not even Sonny Bono can change the premise that the copyright system, as one of the few exceptions to the basic rule that people are free to publish whatever they want, is designed to be a financial inducement, and not a cudgel to keep people from messing with your ideas. Salinger has no more right to tell someone that they can't write a book using his concepts than the heirs of Robert Burns could have told Salinger that he had no right to repurpose "Comin' Through the Rye" for his own creative ends.