Human societies have no great concern for the agency of animals while artificially inseminating them, castrating them -- or, most obviously, killing and eating them.

Till the week he was hanged, William Potter had been a most respectable man. “Weake and infirme” at 60, court records tell us, he had helped found the Puritan colony of New Haven in 1638, helping God’s law to be realised on earth. He was also a member of Reverend John Davenport’s church, a congregation of the most pious and upstanding of the colonies.

But, Potter was also a man with secrets. One morning in 1662, his teenage son discovered them, when he chanced on his father in a barn having sex with a pig.

In what must be among the most bizarre confessions in legal history, Potter led his wife through their livestock, pointing out every animal he had sex with. Two heifers, a cow, three sheep and two sows were hanged with him the next morning.

Last week’s Supreme Court judgment decriminalising homosexuality has been hailed, correctly, as a significant step forward for individual liberties in India. But the judgment has retained one feature of the colonial-era Section 377: sex with animals remains a crime. This part of the landmark decision attracted no comment. Even for the most committed liberals bestiality is a step too far.

From free speech to pornography, or caste and religion, our most vital national debates centre around the conflict between individual rights and social convention. Laws in liberal democracies ought to seek to prevent demonstrable harm to individuals or societies -- not to criminalise individual choices, no matter how outrageous they are.

Precisely because it so deeply repels us, bestiality is a useful prism to examine the principles at stake.

For many, the key argument against bestiality centres around consent. Humans, heterosexual or homosexual, can consent to sex, animals cannot communicate their choice. Leaving aside the one large exception—India’s reluctance to criminalise marital rape, since consummation is the core of marriage under Hindu religious law -- consent is the keystone of democratic sexual ethics.

Paedophiles are criminals because they have sex with children, who cannot offer informed consent. The law on rape, similarly, emerges from the idea that no human being ought to impose their will on another’s body. Animals cannot offer consent, the argument goes, and thus bestiality ought to be criminal.

But this argument rests on shaky philosophical foundations. Human beings can have insights because of their shared experience into the will of another human -- adult or child. In the case of animals, though, it’s simply impossible to know. Indeed, there is no way of knowing if the term consent has any meaning for animals.

The philosophical problem was illustrated by Thomas Nagle in a seminal 1974 paper, asking if humans could understand the experience of being a bat. Humans, Nagle argued, may “imagine that one has webbing on one’s arms, which enables one to fly around at dusk and dawn catching insects in one's mouth; that one has very poor vision, and perceives the surrounding world by a system of reflected high-frequency sound signals; and that one spends the day hanging upside down by one's feet in an attic”.

But, Nagle noted, this “only tells me only what it would be like for me to behave as a bat. But that is not the question. I want to know what it is like for a bat to be a bat”.

The second, more plausible, argument against bestiality is that it is cruel to animals. The evidence on this is, at best, mixed. In 2012, Vice magazine documented the ages-old practice of men in Cartagena, Colombia, having sex with donkeys. The subjects of the documentary demonstrated what can only be described as loving affection to their animals; the animals, in turn, showed no evident distress.

Enumclaw—close to Microsoft’s Seattle headquarters—saw a notorious 2005 case, where a luxury ranch-house was discovered to be serving as a kind of brothel for rich zoophiles from across the world. No animal-cruelty charges were brought. The only victim, perhaps ironically, was Kenneth Pinyan, who was killed while having anal sex with a horse.

Lack of distress, of course, might not amount to consent. But, it is surely significant that the case for animal consent is raised only—only—in the case of sex. Human societies have no great concern for the agency of animals while artificially inseminating them, castrating them -- or, most obviously, killing and eating them.

Though laws do mandate that slaughter be humane, that caveat could just as easily apply to sex; it cannot be a rational argument against bestiality per se.

Even though some opponents of bestiality add to this argument a third claim — that it is unnatural — this proposition is demonstrably untrue.

Zoologists have documented monkeys mating with deer, and fur seals seeking to mate with king penguins. Genetically-close species, like coyotes and wolves or grizzly bears and polar bears, even give birth to offspring. Humans share Neanderthal DNA, making it clear the two species interbred when they encountered each other in Eurasia some 40,000 years ago.

There is, it ought to be added, nothing “natural” about many human sexual practices which are not criminalised. Consider, for example, the use of sex toys, or for that matter condoms.

For insights into what really underpins our revulsion against bestiality, we must gaze deep into the history of our darkest fears.

“And if a man lie with a beast,” the Old Testament reads, “he shall surely be put to death; and ye shall slay the beast”. From the 1640s, the New World was convulsed by a new ideological terror over the unremarkable practice of having sex with farm animals. The colonies had large populations of single men; communities worried that the Devil was seducing them into behaviours that would draw God’s wrath. Bestialists were thought to have been seduced by the Devil.

“Bestiality”, the historian John Murrin has argued, “discredited men like witchcraft discredited women”. Between 1642 and 1662 New England executed six men for bestiality—the same period it hanged 13 women and two men for consorting with the Devil.

People widely believed that intercourse with animals could produce monstrous offspring. The fantasy was a durable one: in one 1812 case, prominent politician William Molton was accused of having sex with a bitch who then delivered puppies with “large heads, no hair on them nor tails, and on the side of their head they had small ears”.

Gay sex was also relentlessly persecuted.

In 1646, New Haven hanged William Plaine, a married man, for having sex with two men. He had, it was recorded at his trial, “corrupted a great parte of the youth of Gilford by masturbation, which he had committed and provoked others to the like, above 100 tymes”. Even worse, “to some who questioned the lawfulness of such a filthy practice, he did insinuate seedes of Atheism, questioning whither there were a God &c.”

India, unlike the Puritans who colonised America, has little religious baggage around bestiality. Ancient art tells us our ancestors saw bestiality as just one more of a wide array of sexual practices. Temple sculptures from Ballegavi, Barsur, Nada-Kalasi and Khajuraho contain explicit images of humans having sex with animals, rendered without judgment. Legend is replete with trans-species forms: Rishyashringa, for instance, is said to have born to a deer by a hermit, or Vishnu as Narasimha.

Even the laws of Manu prescribe only that men guilty of “a bestial crime, or an unnatural crime with a female, or has had intercourse in water, or with a menstruating woman”, expiate themselves by the rite of samtapana kirkkhra -- a minor punishment that required subsisting for a day and night on cow urine and dung, along with sour milk, ghee and a decoction of khus grass.

Puritan attitudes toward sex, born of a desire to punish individual choice and ensure social conformity, were transported to India by the British, expressing themselves in Article 377.

The simple truth is: like so many behaviours most of us find repulsive, bestiality is an individual choice. How far societies are willing to concede the right to act on that choice is a good measure of the integrity of their democratic convictions.