You are right. It has nothing at all to do with duplication or how easy it is. One of technology's greatest and most subtle tricks is the elimination of scarcity. Its not that I can take one for myself (no matter how easy or hard it might be), its that when I do, I don't take yours. It up-ends the economic apple cart in a way that is very non-intuitive and difficult for the human mind to grasp via "common sense".
Its easy to comprehend a lower and lower marginal cost per unit but once that cost reaches the zero limit, it seems that the formulas that our current economy depend on become undefined.
Technology doesn't invalidate the rights of owners/creators, it forces us to completely reevaluate what ownership means. How to "pay" the author might not even be a meaningful question in the economy that results.
We are fortunate that we get a long trial run on things as frivolous as music and moving picture stories before rep/raps bulldoze us on their way through to Star Trek replicators.