In the classic SD column at http://www.straightdope.com/classics/a1_239a.html, unca Cece says:
Yes, from my experience, survivalist magazines and “preparedness” stores do tend to overcharge. So, I waltzed on down to my local General Nutrition Center (GNC) store, and … discovered that GNC doesn’t carry potassium iodide.
I wondered why, until I realized who the target demographic was for GNC stores in the first place.
GNC primarily sells vitamin and mineral supplements. Their primary customers are the same types of people that frequent health food stores. Of those people who buy health food, the overwhelming majority are left-of-center politically.
However, potassium iodide is no ordinary vitamin or mineral supplement. It’s supposed to allow you to better survive the radioactive fallout from a nuclear strike. Most of the people who are interested in potassium iodide are survivalists – and the overwhelming majority of survivalists are right-of-center politically.
Since GNC’s main product lines appeal to people on the other side of the political spectrum from the usual survivalists, they probably get very few survivalists in their stores. Therefore, it would not be profitable for them to stock survivalist items, therefore, they don’t carry potassium iodide. Q.E.D…