First, how do you prove that mankind is invested with the right of killing them, and that brutes have been created for the purpose you assert them to be? Secondly, it is to be observed that the flesh of man himself possesses the same nourishing and palatable qualities? And are we then to become cannibals for that reason?
Moral Inquiries on the Situation of Man and of Brutes, edited by Peter Singer (Fontwell: Centaur Press, 1992), p. 84.