> She probably would have sold a few copies before you'd be able to do that; and maybe you could produce a slightly modified version that would be better.
I don't even know what "better" means in the context of works of art. In any case it's about money: You would see it justified to cash in on someone else's work after she "sold some copies"? Also this remembers me of the common practice of the ripoff: "hendrix' greatest solo's": not mentioning that they were recorded by john doe .
> It's worth noting that some of the best works of mankind were produced when no copyright was in place, so the argument that associates copyright protections with content creation is weak at best.
It is not weak for that reason. Currently works which are commonly copyrighted nowadays are reproduced very easily: lossless copying, printing, electronic editing etc. Try that with the sistine chapel. You would have to clone the Borgias first. Quoting is indeed very common in art but it does not compare to copying. I think that the circumstances are not comparable.
> Derivative works are authored all the time.
Yes. See above. But selling Harry Potter with some changed scenes is a ripoff and not a derivative work.
> Most of what Disney ever produced is derived from popular classics from the 18th / 19th centuries (I remember that in "The Hunchback of Notre-Dame", the original author, Victor Hugo, isn't even credited)
Completely agree. Disney is indeed fishy what concerns his copyrights based on other's efforts. But honestly: when and why should you be able to cash in on coffee mugs showing disney's rendering of the seven dwarfs?