That would probably depend on whether they were minarchist or anarchist libertarians. Minarchists would likely defend copyright with more rational time limits, whereas anarchists would contend that copyright is not rational or enforceable, and that artistic patronage is the only viable business model.
In either case, "stealing" an artistic work would be interpreted as plagiarism rather than unauthorized copying.
Artists capable of doing live performances could also sell tickets, I suppose. Authors might be paid to attend conventions and book signings. Without copyright, the works are disseminated widely to generate a fan base, and the revenue is derived from the truly limited resource: the artist's time.
Plagiarism is passing someone else's work off as your own. Unauthorized copying is just providing a work for others to consume without claiming credit for it, but without having a legal right to do so. Plagiarism doesn't really relate to authorization at all. If you have permission from someone to put your name on their work, that doesn't change the fact that you are lying, which can have consequences of its own (especially in an academic context).
I thought this was obvious, but maybe it isn't? I see disclaimers on Youtube all the time ("I don't own this") which seem to imply the person posting the video doesn't understand the difference.
I remember reading an article about this phenomenon, and arguing from that "plagiarism" as a concept will eat the "copyright" concept. unfortunately i cannot find it right now.
Bringing it back to the root discussion that once you remove the requirement for authorization to copy works, there aren't many ways left to steal IP other than intentionally stealing the authors reputation, which more or less is the full official definition of plagiarism. Which you can do perfectly well by miserably failing to properly document a source, not just claiming you authored it. If I claim I wrote your post, that isn't treated all that differently than if I claim PG wrote your post.
Also muddying the waters is most plagiarism definitions include some level of intentional act, not just Fing up. Negligence is a super fuzzy area. So accidentally citing you as Qubix because I've played the board game is more or less OK. Incompetent, true, but not plagiarism.
Note that SOME people insist on getting all wound up about self plagiarism which can be a fraudulent act, but is not exactly real plagiarism, they just kind of borrowed the name because it sounds evil. Much like the multiple and peculiar definitions of computer "hacker" which have very little to do with each other aside from sounding impressive. Self plagiarism has nothing at all to do with plagiarism, other than both coincidentally being more or less wrong.
In either case, "stealing" an artistic work would be interpreted as plagiarism rather than unauthorized copying.
Artists capable of doing live performances could also sell tickets, I suppose. Authors might be paid to attend conventions and book signings. Without copyright, the works are disseminated widely to generate a fan base, and the revenue is derived from the truly limited resource: the artist's time.