I know I will get blasted for this. First I want to say I admire vegans, vegetarians and anyone who is diligent about their diet. My point is, we are a part of a self sustaining ecosystem as are animals, fish, plants, bugs, bees, etc. What are animals here on earth for? Not to look at cuz they are cute. They are here to be used (for lack of better word).
As far as the argument that if we fed the grain to the people...First of all, the grain they feed to the animals isn't people food quality - would not be consumed by humans. Consumers are very picky. Only a small percentage of agriculture products go into the food system. The majority are produced for industry and to feed livestock. Also, the grains that they feed to the animals are not usually produced using irrigation. Corn, soybeans, wheat, etc are up to good old mother nature for hydration. I am not a farmer but, I work in the finance end of the agriculture industry so have a slightly higher than normal exposure to all things Ag.