How about consent? Village Voice columnist Norah Vincent argues that homosexuality is permissible because "sexual acts between consenting adults should be beyond the prurient reach of the state." However,
When someone has sex with an animal, he foists himself on a creature that has the mental and emotional capacity of a child. Thus, it is no more capable than a child of giving meaningful consent. … [I]f you have had sex with someone who is constitutionally incapable of giving anything that might constitute meaningful consent, you have committed rape. At the very least you have taken advantage of a creature over which you exercise considerable power.
Now we're onto something. The evidence that consent is morally essential—and that animals don't really give it—comes from zoophiles themselves. Dearest Pet reportedly suggests that many artistic images of male animals penetrating women are fantasies projected by men. The usual scenario, according to more reliable records cited in the book, is a man penetrating an animal for his own satisfaction. Singer essentially concedes his vulnerability on the consent issue by ducking it. He defends one scenario in which a dog tries to mount a human visitor's leg, and another in which an orangutan grabs a female attendant. Each scenario presumes the animal's initiative. Likewise, Buble goes through a dog-and-pony show to persuade people that his pet consents to their putative marriage. His letter to the judge included, next to his signature, a paw print purporting to represent the signature of "Lady Buble." But in forging his partner's consent, Buble screwed the pooch. Readers of the letter recognized that the paw print had been drawn by hand, and a Daily News reader discerned another discrediting detail: "I also noticed in the picture of Buble and his Lady that the Ms. wears a choke collar. A willing participant indeed."
So one mystery is solved. If you want to say that contraception, sodomy, and homosexuality are OK but sex with animals isn't, you can stipulate (as Slate's "Chatterbox" does) that sex is permissible only if both parties consent to it. This still leaves you with the problem of explaining why it's OK to kill and eat animals. But two other mysteries remain. One is Singer's position on consent. Does he think sex without consent is immoral? What mental capacities are necessary to give consent? Do animals have those capacities? Who else has those capacities? This line of questioning converges with the other mystery. "One by one, the taboos have fallen," Singer writes in his review of Dearest Pet, building up to the subject of zoophilia. The book's publisher calls sex with animals "the last taboo." But it can't be the last taboo, because there's another subject on which Singer, while freely discussing the charms and merits of zoophilia, seems strangely muzzled. The telling issue—the dog that didn't bark—is pedophilia.
A philosopher's duty is to clarify his principles and defend their consistent application. Those who embrace the principle of consent, and who agree that an animal "is no more capable than a child of giving meaningful consent," have done both. They have stated their principle and applied it to sex with children. What about Singer? He has often compared the mental ability of higher animals to that of children. Does he think this level of comprehension is sufficient to give consent to sex? If the answer is no, isn't zoophilia wrong? If the answer is yes, isn't pedophilia OK? Dog paddling, an old dog's new tricks, dog-eat-dog, a three-dog night—that's kid stuff. You want to take on a real taboo, Professor Singer? Stand up and be a man.