I hope you're joking. Shopped there tonight. It was there or a poorly stocked K-Mart. I find the local grocery store less ethical than the Walmart.
If your audience does shop at Walmart, or knows people who do, then pointing out Walmart's jaw dropping numbers will not be a good device for illuminating the importance of market validation. In fact it could encourage them carry on with the potentially mistaken assumption that the entire planet's needs/problems are the same as their own.