As far as I can tell, a retail pharmacy’s role is to dispense medication per a prescription, while avoiding errors caused by mixing medicines and advising people how to take medicine.

A retail pharmacy’s role is not to be the de facto front line workers for the DEA. So when our government collects fines from businesses for not policing their customers, expect the business to start discriminating against the customers, due to the lack of liability shield the government has.

An even simpler way to put it is, why would a business that earns money selling things want to sell less of those things (legitimate prescriptions)? The answer has to be the risk of selling is too high.