> Second-order effects are real - removing copyright would hurt authors.

Aiding authors is an instrumental, not fundamental, purpose of copyright in the US; the fundamental purpose to which any instrumental purposes are subordinate is “to promote the progress of science and useful arts”.

That is, while copyrights are a form of property, they are not something that is seen as natural property, but instead property explicitly granted as a means of achieving a public policy goal, and therefore limitations (or even elimination) harming the owners of that property is not the kind of dispositive argument against a policy that would be with the kinds of property seen as natural property.

To make this more explicit, the argument is that removing copyright hurts authors, meaning that fewer people become authors in the future, meaning that the progress of the useful arts is hurt.