Making Wal-mart a party to food waste is a great way to harm the corporation. Any animal rights activist will agree that a cow or pig dying for schadenfreude is only marginally worse than a cow or pig dying to feed someone.
Wal-mart doesn't care about waste - I doubt any big corporations do. What Wal-mart does is just pass along that cost to every other customer, and in the end that is the only person you are hurting.