The words of Pierre-Elliot Trudeau, former prime minister of Canada, that “the state has no place in the bedrooms of the nation”, are frequently being trotted out lately. They’ve been used to argue for legalizing same-sex marriage and polygamy; to argue against any restrictions on new reproductive technologies; and to argue that the criminal law should not be employed to prosecute knowingly placing a sexual partner at risk of the transmission of HIV. Most recently, they were used in a discussion, on "The Current", a show on the CBC network, about decriminalizing incest.
Article 155 of the Canadian Criminal Code provides:

(1) Everyone commits incest who, knowing that another person is by blood relationship his or her parent, child, brother, sister, grandparent, grandchild, as the case may be, has sexual intercourse with that person.
Punishment
(2) Every one who commits incest is guilty of an indictable offence and liable to imprisonment for a term not exceeding fourteen years.

Incest is not a crime in all countries, for instance, in France, the Netherlands and Brazil. Romania is considering decriminalizing it, while Sweden only prohibits siblings getting married. In other countries incest is illegal with a wide range of severity of the penalties. Arguing for and against decriminalizing incest Some people are proposing that just as laws criminalizing homosexual acts or limiting marriage to monogamous heterosexual unions have been changed, the law against incest should be repealed. They argue this law is outdated, does not reflect current social mores regarding sexual activity, and is nothing more than imposing some people’s view of morality on others in a context where personal privacy should take priority.
Underlying their approach is the belief that personal preference is the guiding principle regarding one’s sexual activity and that what one does, as long as it’s among consenting adults, causes no harm to anyone else.
Their definition of harm is very narrow. Any concern about harm to children who might be conceived as a result of incest or the harm it does to family structure, relations and functioning, and, thereby, to society and its values, is not on the radar screen. So, if a grandfather wants to have sex with his 18-year-old granddaughter and she consents, it’s no one else’s business except their’s.
Those making the case for legalizing incest reject the idea that incestuous conduct might be inherently morally wrong. Rather, moral relativism governs, that is, the decisions of the persons involved as to the ethics of their conduct are conclusive. Ethics becomes nothing more than personal preferences.
As is true for same-sex marriage and polygamy, incest raises the question of whether what constitutes a family should also be just a matter of personal preference. Or, do children have a right not to be born from an incestuous relationship and a right not to have to live in a family constructed around such a relationship?
What should children not be faced with in this regard? For instance, imagine a family in which a young girl has three older brothers. Will she grow up wondering which one or more will want to have sex with her when she is 18 years old? The incest taboo The incest taboo is long-standing and widespread across all kinds of societies, cultures and religions. That can be taken to indicate that it is not just a cultural phenomenon, but has some deeper base and is not merely a relic of an outdated human morality.
In Primeval Kinship, Quebec’s distinguished primatologist Bernard Chapais, challenges the view that the incest taboo is a human construct. According to Chapais, “incest avoidance” is a pervasive and generalized phenomenon in all primate species. That indicates that it probably has a genetic base and other research that it might be an epigenetic phenomenon.
Epigenetics is the new field of research that explores how genes and environmental triggers interact to imprint (activate) certain genes, which could explain the findings of Finnish anthropologist, Edvard Westermarck.
He showed how people who live in close domestic proximity during the first few years in the life of either one are desensitized to later close sexual attraction. This “Westermarck effect” has been observed in biologically-related families and non-biologically-related ones, for instance, in the Israeli kibbutz system – we treat as kin those we grow up with. So might the incest taboo be the outcome of the imprinting of a gene that reduces sexual attraction to those in our close family with whom we have contact as children?
Because the children of close blood relatives are at greater risk of serious genetic disease and disability, this phenomenon would confer an evolutionary advantage, at least at the level of society in general. I suggest that the legal prohibition on incest is the cultural construct that supports and promotes that advantage. In short, the incest taboo is not just an arbitrary cultural whim, but is a cultural construct based on a biological reality.
Like limiting marriage to monogamous, opposite-sex couples, the incest taboo can be seen as primarily meant to benefit children, not adults, and to do so at the cost of some adults’ freedom of choice regarding their sexual partners and family structure. It’s an example of where the needs and protection of children, and society fulfilling its obligations in that regard, take priority over individuals’ preferences.
Even some people who advocate decriminalizing incest admit that they have a “yuck factor” response to it. This can be an expression of a moral intuition that there is something ethically wrong in the conduct that causes that reaction. We need to listen to our moral intuitions and, as recent research shows, “examined emotions”, not just our cognitive reason, in deciding what is and is not ethical.
In conclusion, we need to keep in mind that an important function of the criminal law is to establish and uphold our most important collective, shared values. And, paradoxically, that role of the law is more important in a secular society than in a religious one, because in the former the law is one of the few games in town available to do that. Margaret Somerville is director of the Centre for Medicine, Ethics and Law at McGill University.