I know there's more nuance to this - you can disagree with what a firm does in a free market economy and assert it's bad for society. But it seems like, from a libertarian perspective, the focus should be on how this is bad for the university, and will reduce its signaling value to employers or something. Because if the customers want a diploma mill, and there's no self-interest downside to the university becoming a diploma mill, then in a libertarian worldview it's generally quite right and good that the university becomes a diploma mill.