Dogfish, it sounds like you are trying to make a larger philosophical point, but you seem to agree that adding arsenic to chicken feed is a bad practice. Do I have that right? If so, I agree with you on both counts. People often misperceive risks, and are much more concerned - and more likely to take action - about trivial risks than the larger but commonly-encountered risks. Sometimes that works out for the best anyway; for example, even though the arsenic in chicken meat presents very little health risk to consumers, if concern over that trivial risk causes growers to stop using Roxarsone, it's a big environmental win - because the real problem is applying 2 million pounds per year of arsenic to farmland and garden soils (through the chicken manure).
I apply the same logic to "organic" food and feeds: the incremental change to personal health is negligible, but the environmental benefit to soils, water, wildlife, and people in argricultural areas (where chemical applications are concentrated) is immense. In effect, those who buy organic food (and chicken feed) are basically paying for the slow cleanup of the agricultural environment.