The economist-headed detractors tended to boil everything down to companies charging higher prices in order to give money to charity. They then explain that this doesn't work because it is proven that customers will buy the ethical option online if it is of equivalent value and price.
Being from a marketing background, I immediately pricked my ears at the complaint marketers have at hand wavy economists. Even if we ignore the fact that the value of a product is completely subjective & that it is influenced in many ways on some of which have anything to do with the physical product, getting customers to choose your product when it of "equivalent price and value" is the no. one thing a whole heap of companies do. Think how much money goes into ads for washing powder.