Peter Singer's views on animal ethics, often presented in the press as daft and sentimental, are, in fact, I know you agree, hard-headed, logical, and compelling. He starts with the principle of "equal consideration of interests," a form of equality that embraces all humans regardless of their differences, and shows that there is no morally relevant reason to draw the line for its application at our species.
Roughly speaking, non-human animals fall into three categories. Some, like oysters, probably do not have enough of a nervous system to be sentient or to feel pain. Others, like farm animals, certainly are sentient and capable of suffering, yet they have no concept of themselves as beings that exist in time. Still others--chimpanzees, orangutans, and gorillas, and perhaps whales and dolphins too--are close enough to us in their capacities that they aspire to the status of moral personhood. They reason, communicate in sophisticated ways, grieve when separated from mates and offspring. Chimps who have been taught sign language use "me" just the way humans do--they are self-conscious.
"The Great Ape Project" aims at securing the right to life and freedom from torture for this third category. The animals in it have an ability to understand what is happening to them which demonstrably exceeds that of severely retarded humans. Yet, as Singer and others have documented in really sickening detail, their cruel treatment (in medical research) and slaughter seems to carry little moral weight with us. I often wonder how we would treat Neanderthals if they were still a distinct species from us, probably without a spoken language (like chimps, they didn't have the right voice box), yet they were comparable to us in intelligence and appearance. If they had not become extinct, what sort of rights would they have today? Would they be in labs getting injected with the AIDS virus and subjected to lethal doses of radiation? If they qualified as persons, would that strengthen the claim of orangutans, our next closest kin in evolutionary terms?
An interesting fact: In 1906 the Bronx Zoo kept an African pygmy in the same cage with an orangutan. The exhibit was short-lived--not because of the moral outrage, but because the pygmy, named Ota Benga, had a habit of shooting arrows at zoo visitors who made sport of him. On being released he moved to Virginia, where, a few years later, he committed suicide. (The story is told in Pat Shipman's 1994 book The Evolution of Racism.)
As for the merely sentient farm animals, it is worth noting that in all the millennia during which humans have had "stewardship" over them, they have never been treated as badly as they are today in modern agribusiness. The details are in Animal Liberation, and once again, they're really sickening. What justifies all the suffering? We really like the way their flesh tastes.
It doesn't even taste very good. Factory-farmed chicken is scarcely worth eating, as anyone who has ever had a free-range chicken, or been to France, realizes. One might call this the insipidity of evil. Singer is himself a vegetarian, but an eminently reasonable one. He seems to have principled objection to eating the flesh of sentient (but not self-conscious) creatures, provided they are not confined their entire lives to darkened crates, castrated without anesthesia, etc.--the very kind of treatment, by the way, which is prohibited by cruelty to animals statutes for non-factory farm animals. If people stopped eating the products of factory farms, as Singer urges, a huge amount of needless suffering would instantly end, and the quality of the meat we did eat would vastly improve. It's so nice when morality and self-interest coincide.
Has Singer's case moved you to modify your diet, Colin? For my part, from now on the only meat I'm eating is Kobe Beef. Sure, it costs a hundred dollars an ounce, but the steers spend their entire lives being massaged by comely Japanese lasses. Now that's animal happiness.