I'd expect it to decrease the number and quality of books since it limits the number of things authors can write about and people can't write improved versions of other's people's books either.

Imagine what kinds of books we'd end up with if every story had to compete with alternate versions of the same. Over time the 'best' versions of every popular story would emerge and become mainstream. This was essentially how storytelling worked for all of human history until we made it illegal to retell certain stories.