Copyrights, and the idea of intellectual property in general, are an interesting issue for libertarians. Does freedom of speech and of the press include the right to repeat someone else's writings? Or is there a real property interest in ideas?
Copyrights today are intended to allow the author of a work to gain the benefits of the work, presumably encouraging the production of more such works.
That's now how copyrights started. In 17th-century England, copyrights were introduced as a government-sanctioned monopoly for booksellers in exchange for the booksellers' acquiesence to restrictions on freedom of the press. Copyrights were essentially a bribe to reduce opposition to the English government's encroachment on individual rights.
The fact that copyrights are not permanent, but for a specific duration, underscores the fact that they are a matter of privilege not right. Even if one concedes the benefits of having copyrights, the duration of copyrights is still a matter of debate.
The U.S. Constitution specifically authorizes Congress to set the duration of copyrights, but says copyrights must be of limited duration. Congress has somewhat stretched their authority by repeatedly extending copyright durations; if they continue to do so, they will in effect be making copyrights permanent.
In the U.S., copyrights lasted 56 years, until a 1976 law extended them to 75 years. In 1995, Congress lengthened the duration to 95 years.
The "hard-core" libertarian approach to copyrights would be to abolish them altogether, as a government-imposed monopoly. A more moderate approach would be to lessen their duration.
Source: "Free Winnie!" (c) 1995 Michael S. Hart posted May 3, 1995 to the NETTRAIN mailing list.