I regard Peter as one of the great moralists, because I suspect that more than anyone he has helped to change the attitudes of very many people to the sufferings of animals. Peter is a utilitarian in normative ethics, and a humane attitude to animals is a natural corollary of utilitarianism. Utilitarian concern for animals goes back to Bentham, who, presumably alluding to the Kantians, said that the question was not whether animals can reason, but whether they can suffer.
J. J. C. Smart, ‘Reply to Singer’, in Philip Pettit, Richard Sylvan and Jean Norman (eds.), Metaphysics and Morality: Essays in Honour of J. J. C. Smart, Oxford, 1987, p. 192