If a store simply chooses to prohibit firearms from their store "because" I will either not do any business with them, or do as little as possible with them.
Hmmm, you WOULD buy "as little as possible"? You're hedging already.....What do they have at Cosco that you can't buy, albeit with a little less convenience or cost savings, somewhere else? In other words, what is it that is causing you to compromise on your principals? The cost savings, or the convenience?