In an ideal world, people would buy their food directly from the people who grew or caught it, or grow and catch it themselves. But most people can’t do that. If there were a Walmart closer to where I live, I would probably shop there.I suspect Kummer, and most readers, would find this paragraph benignly true. But the first sentence represents what may be the two most pervasive economic fallacies accepted by the public: middlemen (which Wal-Mart is in this context) do not provide a real service, create no "social" value; moreover, self sufficiency is a high ideal toward which we all should all strive. For an extensive explanation of why they're twin fallacies, I refer you to two EconTalk podcasts: one with Duke's Mike Munger on middlemen, and the other, an excellent monologue by GMU's Russ Roberts (who normally hosts) on comparative advantage.
The second and third sentences of Kummer's paragraph reveal why the first is so fallacious. Indeed, most people can't "buy their food directly from the people who grew or caught it, or grow and catch it themselves," not because they are incapable of going to a farmers market to purchase their produce, or because learning the rudiments of horticulture or hunting and fishing would be too difficult, but because doing so is extremely costly. Costly, not only because farmers markets tend to charge higher prices, but because time is man's most precious resource.
What Wal-Mart and (to a lesser degree) Whole Foods provide is convenience, places where consumers can purchase their locally grown produce and other goods they need (in Wal-Mart's case, goods as diverse as sunglasses, Wii games, and towels), thus saving them time (and cash). Even in an "ideal" world where we're all immortal beings with no regard for time, the gloriously austere self sufficiency of growing one's own arugula requires effort that would be akin to drudgery for many. A moral failing on their part? Maybe Marx would say so.
Some people enjoy going to farmers markets. That's fine. Some take pride in the bounty of their backyard gardens. That's great, too. But these activities are enjoyed as ends in themselves, as hobbies, or for the warm-and-fuzzy feelings they provide. Ask a single working mother if she would prefer waiting until Sunday to buy her family carrots from a farmers market, or to grow them herself, rather than driving to the local Wal-Mart or Whole Foods after work. Her answer is why Wal-Mart and Whole Foods provide a genuine service, why they create value, and why they should be celebrated, not vilified.