answer:There’s no question that as consumers we’re often gulled into buying things that we don’t “need” (and in fact, many times duped into buying things “for our own good” that are actually harmful to us), but… so what? I don’t quibble over the cost of floss, and I won’t even with the presentation that you’ve made here. Dental floss is useful to me, in the same way that toothpicks are, for cleaning things from between my teeth that I can’t clear by brushing or simply wedging out with my tongue. You’re right that the cost is minimal and the margins seem pretty high (I would expect that the unit production cost for the package you’ve described is lower than 15¢ by an order of magnitude), but I’m not sure whether that cost includes all of the overheads necessary to maintain and store all of the product in sanitary condition, nor the carrying cost for unsold units and WIP. (And it completely ignores costs due to drop-offs in consumer demands based on color, scent / taste, packaging and branding choices. There’s a lot of risk in “fashion”.) Aside from all of the foregoing, it may not be entirely ethical to run a controlled experiment on the efficacy of dental floss by enjoining people from using it if you think that it actually helps to eliminate tooth decay. That is, as a medical experimenter, if you think that curtailing use to a control group would lead to decreased oral health, then how could you ethically participate in that experiment?