Copyright (and that's what it is, copyright), in western societies, has always been seen as something that was granted by the government for a limited period of time, in order to provide benefits to both the creator and the public. Copyright allows the creator to realize gains from the creation. The limitation on the duration of copyright has two purposes: one, it allows the public eventually to be able to freely incorporate previously-created material into new works; second, it is incentive for the creator to create new works and not just laze around (and even his descendants to laze around!) forever because of the good fortune to have created one fabulously successful work.
I agree with you; it is the right to copy, and it is called intellectual property for a reason; because it isn't a physical house or acreage; it exists rather all over the place in perhaps millions of widely distributed copies. Most of Shakespeare's plays would never have been written if endless copyright laws were in place during his time; as most of his works were derivative, being drawn from old literature that he brought into the medium of theatre. The copyright for Oscar Wilde's work ran out in recent years, and because of that there have been a lot of new movies made from his plays, even lesser known ones never filmed before; I think that is a great thing. Wilde's works, like Shakespeare, Shelley, and the Bronte's are historical cultural resources, not belonging to any one person. And that is good, because people are free to interact with them, translate them, and reimagine them as they wish.