An enormous volume of material has already appeared on the conditions under which animals live and die on factory farms, and more is almost certainly on the way. Much of this material is upsetting in the extreme, and it is difficult to imagine any normal person reading or hearing of it without being revolted. Indeed, our feeling of revulsion may be so intense that we simply can no longer bring ourselves to eat meat. In other words, we become vegetarians, not through any decision of principle, but through being unable to bring ourselves to continue to dine upon the flesh of animals. We become vegetarians in this way, however, only if we are revolted to a degree sufficient to overcome our fondness or liking for meat; and whether we are going to be sufficiently revolted by what we read and hear cannot be known in advance by the advocate of vegetarianism. If our liking for meat is in fact more intense than our revulsion at the suffering endured on factory farms, then we are going to remain meat-eaters, with the result that, if the vegetarian has grounded his case in an appeal to our feelings, then that case is in jeopardy. In order to protect himself, therefore, he is not likely to rest his case upon (an appeal to) the state and intensities of our feelings.
What the vegetarian wants, surely, is that we should stop eating meat even if our liking for it exceeds our revulsion at the suffering endured on factory farms. And this would seem to be possible only if vegetarianism is based upon principle and not upon feeling. That is, if what the vegetarian wants is that we should stop eating meat even if we like eating it and even if our liking for it greatly exceeds our revulsion at the suffering of animals in being raised and slaughtered for food, then a decision to stop eating meat would seem to amount to a decision of principle. It does not follow that this principle, which becomes the ground or basis of our vegetarianism, will be a moral one; but the overwhelming likelihood is that it will be, in view of the fact that it must convince and compel us to give up eating meat even when our inclinations, habits, and feelings run strongly in the opposite direction. If vegetarianism has a moral basis, a ground rooted in moral principle, then all of us, if we take morality seriously, must earnestly examine our present eating practices, however intense our liking for meat.
(R. G. Frey, Interests and Rights: The Case Against Animals [Oxford: Clarendon Press, 1980], 140-1 [italics in original; footnote omitted])