We have had, for hundreds of years, technology that makes the cost of each marginal copy of a creative work some tiny percentage of what people are willing to pay for that work. Digital technology making that percentage even smaller doesn't fundamentally change anything. There is nothing magic about "essentially zero cost" copies versus "negligible cost" copies.

This is largely because our whole system of property is structured so that marginal cost is broadly irrelevant. We have a pervasive notion in our system that people are entitled to the "benefit of the bargain." That is to say, people are entitled to profit from the difference in price people are willing to pay for something, based on supply and demand, and the marginal cost of producing that something. That's why Apple can sell for $600 iPhones that cost only $207 to produce, or why Louis Vuitton can sell for thousands of dollars handbags that cost maybe $100 to produce. The marginal cost of production is irrelevant, from the buyers viewpoint, in anything we buy. So why should it be different for digital goods?