The initial attractiveness of utilitarianism as a moral theory on which to rest the call for the better treatment of animals was noted in an earlier context. . . . Because animals are sentient (i.e., can experience pleasure and pain) and because they not only have but can act on their preferences, any view that holds that pleasures or pains, or preference-satisfactions or frustrations matter morally is bound to seem attractive to those in search of the moral basis for the animal rights movement. Especially because animals are made to suffer in the pursuit of human purposes—in the name of "efficient" factory farming, for example, or in pursuit of scientific knowledge—the utilitarian injunction to count their suffering and to count it equitably must strike a responsive moral chord. But utilitarianism is not the theory its initial reception by the animal rights movement may have suggested. It provides no basis for the rights of animals and instead contains within itself the grounds for perpetuating the very speciesist practices it was supposed to overthrow. To secure the philosophical foundation for animal rights requires abandoning utilitarianism.
(Tom Regan, The Case for Animal Rights, updated with a new preface [Berkeley and Los Angeles: University of California Press, 2004], 315 [italics in original; ellipsis added] [first edition published in 1983])