Tame animals are better off when ruled by man, and so are those who are naturally inferior when ruled by their superiors.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“From birth, some are marked out for subjection, others for rule; the man who is by nature not his own but another man’s is by nature a slave. Slaves should not be Greeks, but of an inferior race with less spirit (1255a and 1330a) Tame animals are better off when ruled by man, and so are those who are naturally inferior when ruled by their superiors. It may be questioned whether the practice of making slaves out of prisoners of war is justified; power, such as leads to victory in war, seems to imply superior virtue, but this is not always the case.” source