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.
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.