Singer presents what he takes to be an irrefutable, logically cogent argument for animal liberation and against speciesism. Many philosophers hold that a certain reciprocity exists between moral rights and moral obligations; not Singer. His entire argument depends on the use of different criteria to allot rights and obligations. According to Singer, any entity capable of moral judgment is morally obligated to give equal consideration to the interests of any organism that can suffer or experience enjoyment. It just so happens that only human beings are capable of moral reflection; "it makes no sense to hold nonhuman animals morally responsible or culpable for what they do" (p. 250). Many species, on the other hand, can suffer or experience enjoyment. Hence, human beings are morally obligated to give equal consideration to the interests of each other and to many nonhuman animals, whereas nonhuman animals owe human beings and each other nothing.
The asymmetry that results from Singer's using different criteria for rights and obligations hardly seems fair. We owe other animals so much, and they owe us nothing.
(David L. Hull, "The Rights of Animals," review of Animal Liberation: A New Ethics for Our Treatment of Animals, by Peter Singer, Science, n.s., 192 [14 May 1976]: 679-80, at 679)
