You would mark heroin bad because you perceive it to offer no redeeming qualities, but if it was legal, in a store, to buy, marking it as bad would be ridiculous because you have basically damaged the product and therefore create more demand for it and second because nobody does that in the store, in real life, nobody goes to the gun store and marks guns with x because they kill people, nobody goes to the kitchen section and marks knives with a black marker, x, or any other product, people are sensible like dwinblood has pointed out and would not do something like that. Take drain cleaner, sure you can use it for it's intended purpose but if you were bombarded with numerous accounts of people using it to get high (hypothetically) and then dying because of that, then you will also go and mark drain cleaner as bad, therefore damaging the product, creating more demand for it etc? It's pure nonsense therefor, regardless of the fact that heroin does have redeeming qualities and has been used in the past in treating numerous things, as everything has value in various aspects, where as marking x on products you don't want doesn't have value.