Cory Doctorow has a terrific mini-essay up at Boing Boing about the 300th anniversary of modern copyright and the importance of copying.
It's true. We learn by copying. The best storytellers have learned by copying and expanding their favourite tales. We see it in the playgrounds all the time. We see it on fan fic sites. People learning and honing the trade of storytelling will always copy and then reinvent.
Copyright would have devastated the fairy tale. The fairy tale was enriched by copying, adaptation, reinvention. In more recent times, some have turned their noses up at what they perceive to be blatant copying of tales, repining, for instance, that Madame d'Aulnoy simply copied Basile. Yet she didn't. Her tales remain distinct even as she reinvented the tales that Basile possibly himself reinvented (much is lost in the unknown of the oral tradition, to the extent of not knowing if it was in turn an invention in its own right). Competing versions of tales were often the fare of the salons.
The notion of copyright draws very much on a notion of property. Yet ideas and stories aren't property. You cannot measure their boundaries, fence them off, place a sign declaring 'no trespassers'. Much as we try to own and sell ideas and stories, the stories refuse to be pinned down into the terms of a contract.
There must still be fair play. It's only in our own interests to ensure the storytellers can support themselves and blatant plagiarism has always been a callow act. But Cinderella is not a parcel of land or a chattel, either.