What these people never think about is the fact that these animals being edible is what keeps people breeding, raising and feeding them. Cows, pigs and chickens have never been endangered species because they are (or make) good food. I own 30 or so chickens that I buy food for, built a safe coop for, let out into a pasture every morning and close in each night. I do this because they make yummy eggs.
The bison is no longer endangered because people started raising them for meat. A hundred years ago, there were 800 or so. Now there are over 300,000.
If you couldn't use cows for milk or meat, who would spend the money on fencing, irrigation and hay to keep a herd around?