>Intelligence is just one thing we can consider when deciding what's morally acceptable to kill and consume. Genetic proximity to humans clearly matters to many people as well: lots of people stick to seafood and/or poultry despite the fact that octopuses and some birds can be quite intelligent.
Sure, but it's pretty obvious that fish and chicken are very stupid animals, and those mammals are much smarter, so I'm not sure that genetic proximity is as important as you think it is. Octopuses are the only real standout here: they really are quite intelligent, which is even more remarkable because they're invertebrates. And yes, some birds are quite intelligent (like crows), but we don't eat those types of birds (probably because they're just not very good as food).
>cows are smarter than horses, but we choose not to eat dogs and horses because they more readily comprehend and obey our commands
Who's "we"? Horsemeat is very easy to find in restaurants here in Japan. It's not bad if cooked properly, but it's a lot like deer meat. Deer are pretty stupid too (probably about as smart as cows), but they aren't normally eaten either, and it's because most people just don't like the taste that much (it's "gamey"), and it's difficult to cook. Cows taste better than horses because they have a lot more fat.
Also, octopuses have been mentioned here many times, but in the US they aren't a terribly popular food item, whereas here in Japan they're very common (along with squid). So differing cultures and culinary traditions I think have a lot to do with it too, just as with horses above.