Despite being pummeled with this argument at every turn, I have not yet heard a compelling case. The dog-equals-pig argument has some serious flaws. First, individuals and cultures have always made countless decisions about what things are food and what are not. The basis for these decisions is about much more than whether something is edible or palatable. Until recent years, for instance, few modern Americans had eaten dandelions, nettles, or purslane, even though each of these plants (generally considered "weeds") are not only highly nutritious, they're quite tasty.
What each of us eats is the result of multiple factors, including income, geography, climate, culture, heritage, habit, and even, to a certain extent evolution (more on that in a moment), and there's simply nothing wrong with that. Evidently, these norms are the basis for the modern Western view that eating dogs is wrong. It's no more contradictory to eat a pig but not a dog than it is to eat arugula but not purslane. When it comes to eating, we all rule some things in and other things out.
Danish chef Rene Redzepi has made something of an art of bucking this universal system. Interviewed recently by NPR, he discussed why his restaurant and cookbook explore ingredients most of us wouldn't even consider food, such as burnt hay, wood chips, and bulrushes. "We have narrowed ourselves in always using the same [few] ingredients," he explained, adding, "We have a nature and product diversity that needs to be used."
More importantly, the pig-equals-dog claim ignores the glaringly obvious issue of relationships. The human relationship with dogs is unique. For as many as 30,000 years, dogs have literally been indispensible members of the human family. Quite naturally, many humans have qualms about eating a family member.
Most of us have traveled to countries where animals that are not generally eaten in the United States were found on local menus. In France, where I lived for a year, I saw people eating frogs, pigeons, snails, and horses. Some Italians eat donkeys; South Africans eat ostrich. In West Africa, another part of the world where I spent a year, I heard of people eating primates. And in some parts of the world, most notably China, many regard dog meat as not only palatable but delicious.
In Unmentionable Cuisine, Calwin Schwabe reported that dog meat was once also widely eaten and valued in Hawaii. He notes that as recently as a few decades ago, many Hawaiians raised both dogs and pigs as pets and for food and were baffled by why Western visitors found only the pig suitable for consumption.
But the Hawaiian perspective seems to be unique. More commonly, dogs are part of the household while pigs are designated to the fields. Pigs have benefitted humans while dogs were fundamental to their existence. That is to say, people could get by without pigs (by eating other meat, for example), but their success—and, in many cases, their very survival—depended on dogs.