The third dominant justifying theory for intellectual property rights is often called the Self-Expression justification. Most scholars attribute it to Hegel, but it ultimately has roots in Kant. While few philosophers even addressed intellectual property, Immanuel Kant discusses the sale of pirated books in Metaphysics of Morals. Kant argues that reprinting a book after first publication is a violation of the author's right to entrust his communication to a particular publisher. Viewing books as importantly communicative, not material, in nature, Kant claims that a publisher is essentially a spokesperson, someone designated by an author to communicate his ideas to others. Reprinters interrupt this process by taking it on themselves to communicate the author's idea, without his consent. Reprinting is then akin to removing the author's control over the communication of his ideas. While Kant's argument does not get you an entire system of intellectual property, he does draw an association between books, and we can broaden it to include all media, and expressive acts. A book is not simply an object; it is a vessel for ideas. It is the contents of the book, the ideas rather than the material object, that make reprinting a moral issue.
Now, the Self-Expression justification proper comes from a later German Idealist thinker, G.W. F. Hegel. Hegel viewed private property as necessary for the actualization of the will. A rational agent needs a domain in which it can exercise its will so that it can come to understand itself, its autonomy, it's place in the dialectical progression of history. Private property is this domain, so one must understand property not in terms of things owned, but in terms of what those mean to the owner. Intellectual property is an especially interesting case because creative works and inventions are specifically products of rational agency. Creative works serve as expressions of the author's will and reason, so any violation of the work must be understand as a harm to the integrity of the author.
As spooky as some of this might sound, European copyright law recognizes certain “moral rights” of an author. These rights, such as the right to receive credit for authorship, never expire, and bear no exceptions. If interpreted broadly, the Self-Expression justification is perhaps the best argument for an author retaining strong control over derivative works. A fan writing using an author's character in a story takes the character out of the author's control. Something very personal to the author has been manipulated without his knowledge or consent. If some readers confuse for the fan story for the author's own work, they might develop a distorted idea about the author's style and personality. These threats are intolerable on a strong reading of the Self-Expression justification. Now, I hold that there are other concerns at stake that override any sense of threatening the author's integrity, but that's a paper I'm currently trying to publish.
The most obvious concern with the Self-Expression justification is its failure to justify a wholesale system of intellectual property. If you don't see what I mean, think about it like this: you have a lot of furniture in your house. Some pieces you might have had growing up, some you might have gotten from friends or family members, and some you just bought because you needed them. Now, imagine that one morning, you woke up and found that your ottoman, the one that you bought for the cat to sleep on, is missing, and in its place is a pile of money, enough to buy a brand new ottoman. Substitute any personal object you own and don't really care about and mutatits mutandis if the furniture example doesn't work for you. The Self-Expression justification is very plausible when talking about the dining room table you got from your grandparents' house, but much less so when considering that ottoman.
Intellectual property is no different. Some authors pour their hearts and souls into novels, poems, musical compositions, or films. Others are just interested in making money and happen to be very good at what they do. I'm sure many authors find themselves in both categories from time to time. Nevertheless, the Self-Expression justification has the most force when the work has the most personal meaning or significance. When a creative work is an economic product, it's not clear what rights an author would have. One could treat all authors as if their works were expressions of their innermost selves unless they waived their rights somehow (though the moral rights in European intellectual property law simply cannot be waived). In that case, the practice would be instituted for a reason that does not universally apply. Furthermore, it seems bizarre to imagine an intellectual property case being decided in favor of a defendant who argued that the plaintiff “did not really care” about his works. I would hope it isn't the law's place to dictate to us what is art (though they do seem to try), so the Self-Expression justification is only a partial justification for an intellectual property system. Nevertheless, it does get employed in argument about derivative works and fair use.