I think the ethical part may have to do with the following from Wikipedia on commerce:

The diversity in the distribution of natural resources, differences of human needs and wants, and division of labour along with comparative advantage are the principal factors that give rise to commercial exchanges.

I do not see how the commercial part is necessary for the distribution of goods though and recognize it as the main culprit in making such a system unethical. I.e., supplying needs is good and necessary, however a commercial platform is not.