> You don't believe that the creator should have rights over their creation, perhaps because their creation came to you over a medium that allows for easy duplication.
That "easy duplication" is entirely the point. The concept of property is based on the limited nature of physical objects. Land, food, books, player piano roles, and DVDs are scarce resources[1]. The zero-sum nature of scarce objects is where concepts like "theft" and "property" apply. We invented the concept of property to manage scarcity.
When dealing with anything that isn't scarce, the entire concept of "property" doesn't apply. Math, for example - those "ones and zeros" - is non-scarce. Teaching someone that 1+2 is 3 doesn't deprive the teacher future use of addition or the numerals 1, 2, or 3. Most reasonable people would agree that nobody gets to claim property rights over math, because it's a non-scarce idea.
> but that's all it is, a justification.
The unwarranted justification is claiming that unlimited ideas are a scarce resource that requires property rights.
> results in less original content.
Do you also complain that teaching algebra - where ideas are copied from teacher to student - results in fewer novel discoveries in mathematics? Just as teaching math tends to lead to more math discoveries, freely using non-scare stories, sounds, music, images, etc, often leads to more content creation. This is so common we invented terms like "remix" and "cover band" to describe some of the ways media is reused.
[1] https://en.wikipedia.org/wiki/Scarcity