I agree with your argument within the economic context in which your work occurs, it's the only thing that makes many works of art possible. But copyright is a bad thing because the economic context is bad.
If you had all the money you needed, would you stop producing screenplays? I can't answer for you, but I know the answer for me: if I had all the money I needed, I wouldn't stop writing code or performing music. I think the idea that people need economic incentives to do things, especially creative things, is bogus. People don't need incentives to do things, they need their basic needs met so that they can do things. More often than not, the need to fulfill their basic needs gets in the way of people doing the things that they want, and which might prove the most beneficial. I've certainly written reams of useless code to pay the bills instead of open source work that I wanted to do to further humanity. And I'm sure you've spent time doing things to pay the bills when you could have been working on your screenplay.
Of course we don't live in a world where people's needs can simply be met without effort. But the time is coming when no human will have to lift a finger to survive. What incentive will exist then? The structures we have built around the need to earn our survival will prepare us poorly for the world that will be.
I see two futures: one where the robots and artificial intelligences that meet all our needs are owned by the people who bought them and the rest of us are beholden to them, and another where, in the absence of value derived by economic need, we derive value from our feelings, our experiences, our relationships, and our creations. Copyright lives in the former future: the future I want is the latter.