It is this ongoing history of mutual benefit that generates a moral duty of human beings to eat animals. Were the practice beneficial only to one of the two parties, that would perhaps not justify persisting with it. But both benefit. In fact, animals benefit a lot more than human beings do. For human beings could survive as vegetarians or vegans, whereas very few domesticated animals could survive many human beings being vegetarians or vegans. Indeed, if many human beings became vegetarians or vegans, it would be the greatest disaster that there has ever been for animals since the time that an asteroid strike wiped out the dinosaurs and many other species.

Vegetarians and vegans are the natural enemies of domesticated animals that are bred to be eaten. Of course, not all vegetarians and vegans are alike. Quite a few vegetarians and vegans are not motivated by animal rights or welfare, but by a feeling of taboo or pollution – a revulsion at the idea of eating animal flesh. For such vegetarians and vegans, roadkill is off the menu. Unlike the appeal to animal rights or the welfare of animals, this is a reason I respect. But such vegetarians and vegans should admit that acting on these feelings is bad for animals.

Do the motives of carnivores and farmers matter? Typically, they are not high-mindedly concerned with the welfare of animals. But if there are beneficial effects on animals as a side-effect of impure motives, we might think that is all that matters. Or: we might follow Immanuel Kant in distinguishing between treating humans or animals as a means, which may be acceptable, and treating them merely as a means, which is not. So long as carnivores and farmers have the former motives, not the latter, there is no complaint against them.