I think the argument for copyright is basically that it's a way to insure that creative people get paid for being creative. The original intent, at least in the USA, is that it gives the creator a head start. That was much discussed in the Federalist Papers, if I remember correctly. Or maybe it was in letters among the framers of the constitution. It's been a few decades since I was into history that much but I do remember reading about that. It's what got me interested in the question of copyright.
The idea of ownership of something intangible is a bit silly but it's something we agree to accept and acknowledge for a "limited time", silly or not, because it's good for all of us.
The problem today is that "limited time" has been re-defined so that it's now something like 5,000 years after the death of Mickey Mouse.
Barry