Cows and pigs are allowed to be eaten because there is a massive industry lobby suggesting that humans need protein for growth. No one needs that much protein and its just big business now. Shutting it down means job losses and a shrunken economy.

Eating the animal you want to eat is cultural and also depends on what economic class you belong to. In europe, specially france, eating snales and frog legs is ok. I am sure at some point, someone wealthy would have said he wants to eats something unique, a meat not eaten by the commoner.

Some domesticated animals were used as a source of food supply till they found their way on the kitchen table. Some domesticated animals found their way into homes in some cultures. In others they stayed as a food source.

Dogs are eaten in china, india, and korea but it is not a mass market thing. It is poor man's food. You may want to eat a dog if you havent been told as a society that it is wrong. I think where the animal lies in the evolutionary chain also matters.