In Vice is Nice But Incest is Best: The Problem of a Moral Taboo, Vera Bergelson describes five reasons traditionally used as justification for the criminalization of incest, and variations of them are used as criticism of consanguinamorous relationships as well:

  1. Respecting Religion and the Universal Tradition
  2. Avoiding Genetic Abnormalities
  3. Protecting the Family Unit
  4. Preventing Sexual Abuse and Sexual Imposition
  5. Precluding Immorality

Respecting Religion and the Universal Tradition

Consanguinamorous relationship are often criticized as being against the teachings of the Bible, or are said to violate other religions' teachings, and therefore should not be permitted. To the degree that this rationale is used to try to justify laws today, it is not acceptable since it goes against the Establishment Clause, which prohibits making any laws "respecting an establishment of religion". The argument from religion is rarely used by itself today, but rather its often used to underscore the "universality of incest taboo." However, the ban on incest is not universally taboo, as Robin Fox points out that there has been at least 96 societies which have permitted sexual relations between family members, including marriage.[1]

Avoiding Genetic Abnormalities

One of the most common reasons used for the ban of consanguinamorous relationships is that the ban prevents inbreeding, which can have a higher rate of genetic defects in offspring. Supporters of consanguinamory argue that this line of reasoning has several flaws:

First, if this were the reason to ban consensual incest, then the ban would be overly broad since it doesn't just apply to reproduction, and many consanguinamorous couples choose not to have children, and use contraception to avoid having them.

Second, incest laws apply not only to blood relatives, but also to step-siblings and adopted relatives, in which case inbreeding does not have any higher risk of genetic defects than in the general population.

Third, its not at all clear that inbreeding presents a threat to society. Because of the Westermarck effect, the number of people who are open to consanguinamory is quite low, and many consanguinamorous couples choose not to have children from sexual reproduction with each other. In addition, the number of serious genetic disorders associated with inbreeding is quite limited.[2]

Fourth, there is the question of who exactly is harmed by inbreeding. Intuitively, one may say the child is harmed, however this is debatable given the "non-identity problem". Suppose a child named Frank has been born of inbreeding and happens to have a genetic defect that degrades his quality of life. This raises the question: Could the parents have done anything better for Frank? If Frank's mother had had sex with a different person, she would have had a different child, and Frank wouldn't have existed. For Frank, no alternative was possible - he could not have failed to have these genetic defects.

Finally, under no other circumstances does the law penalize people for producing genetically defective offspring. As Bergelson writes:

We do not require people to be tested for genetic abnormalities as a condition of granting them a marriage license. We do not prohibit procreation by people known to possess a defective gene. A law criminalizing child bearingby the deaf-mute or by dwarf partners would most certainly cause public outrage. More-over, the early prenatal diagnostics today often give prospective parents the option of aborting an abnormal fetus. If they choose not to exercise that option, they act with a much higher degree of subjective responsibility than an incestuous couple having unprotected sex."[3]

And Johann Hari writes:

We should, however, be wary of damning incest on these grounds alone. To prohibit two people from having sex because their offspring may be "defective" or "inferior" is to adopt the standpoint of a eugenicist.[4]

Protecting the Family Unit

Another common criticism of consanguinamory is that it threatens the nuclear family:

The essentials of a nuclear family are a man and a woman in a relation of sexual intimacy and bearing a responsibility for the upbringing of the woman’s children. This institution is the principal context for socialization of the individual. A critical component of that process is the channeling of the individual’s erotic impulses into socially acceptable patterns.[5]

According to this line of reasoning, prohibiting consensual incest is justified because it preserves the nuclear family by preventing sex rivalries and jealousies within the family unit, and by ensuring suitable role models it prepares children for future familial responsibilities.

While it's true that sex rivalries and jealousies can be destructive to the family, so can other non-sexual rivalries and jealousies. And the question of who gets the family inheritance can be equally destructive. And divorce is almost by definition destructive to the family unit, yet divorce is not illegal. There has been a long history of rivalries within families throughout history, including those documented in the Bible, and yet all of these have not destroyed the family as a social institution.

Next, if two siblings chose to have sex and form a relationship, sending them off to prison for years is also very destructive to the family.

Preventing Sexual Abuse and Sexual Imposition

Another criticism of consanguinamorous relationships is that they are a form of sexual abuse, or often have a power imbalance that makes them not truly consensual. Consanguinamorous relationships are by definition loving and intimate relationships between consenting adults, in which no sexual abuse exists, so the first part of this criticism clearly isn't valid.

The second part of the argument is usually explained by saying that an adult parent can still have some power over his or her adult son or daughter, such as when the adult child is still financially dependent on the parent, and thus an intimate relationship between them is not truly consensual, and therefore incest should be illegal. However this fails to account for the many consanguinamorous relationships between siblings close in age, or twins, in which no power imbalance exists.

Additionally, the law doesn't forbid relationships between other adults with a large age gap, or between a very wealthy person or very poor person, or between one person who works full time and another person who is financially dependent on him or her, or between a very strong person and very weak person. If legislators tried to introduce a law that would prevent all new marriages except for marraiges between people who were within a few years of age, who were from the same social class, who both proved they were financially independent, and who had close to the same physical strength and intelligence, there would be a public outcry.

Precluding Immorality

A final criticism of consanguinamory is that its simply immoral. While the majority of people currently view consensual incest as immoral, many people view it as permissible and have strong arguments to justify their views.[6] There is a wide variety of cultures and moral views in the world, and people who view consanguinamory as immoral can simply choose not to pursue consanguinamorous relationships. The question of whether the morals of the majority is a legitimate basis for the criminalization of consanguinamorous relationships is a legal question.

The enforcement of morals through laws as for a long time been viewed as a valid function of the state, however it has also been criticized as going against the liberal tradition in both principle and in practice, since it requires infringing on a citizen's liberty and privacy. By the early 21st century, views on criminalizing private conduct on the grounds of immorality reached a turning point, as Bergelson writes:

In Lawrence v. Texas, the United States Supreme Court held that a Texas statute prohibiting homosexual sodomy was unconstitutional insofar as it applied to the private conduct of two consenting adults. The court admitted that for centuries homo-sexual conduct was condemned as immoral, and for a number of people it is still completely unacceptable. Yet, these considerations were held to be insufficient for criminal prosecution: even if anti-sodomy laws are grounded in ‘‘profound and deep convictions accepted as ethical and moral principles’’ by many people, the majority may not ‘‘use the power of the State to enforce these views on the whole society through operation of the criminal law.’’

This says that even if the majority of people view something as immoral, this is not sufficient justification to use the power of the State to enforce these moral views on others through the criminal law. And in Lawrence v. Texas, Justice Kennedy wrote the following regarding the case about the homosexual couple:

The present case does not involve minors. It does not involve persons who might be injured or coerced or who are situated in relationships where consent might not easily be refused. It does not involve public conduct or prostitution. … The case does involve two adults who, with full and mutual consent from each other, engaged in sexual practices common to a homosexual lifestyle. The petitioners are entitled to respect for their private lives. The State cannot demean their existence or control their destiny by making their private sexual conduct a crime.
And Justice Scalia wrote the following on the decision to end the prohibition of homosexual acts:

|The Texas statute undeniably seeks to further the belief of its citizens that certain forms of sexual behavior are ‘‘immoral and unacceptable,’’—the same interest furthered by criminal laws against fornication, bigamy, adultery, adult incest, bestiality, and obscenity. Bowers held that this was a legitimate state interest. The Court today reaches the opposite conclusion … This effectively decrees the end of all morals legislation.

Zhou writes that "careful examination of Lawrence’s reasoning reveals that sexual intimacy must also encompass sexual relationships between first-degree relatives."[7]

Thus supporters of consanguinamory argue that there is legal precedent for not enforcing the morals of the majority on everyone, especially in cases regarding what two consenting adults chose to do in private lives, and so even if many people view consanguinamorous relationships as immoral, that is not a justified basis for the criminalization of loving relationships between consenting adults who are related.


  1. Fox, R. (1980). The red lamp of incest. New York, NY: E.P. Dutton.
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  5. MPC, § 230.2, cmt 2(c) at 406 (Official Draft and Revised Comments 1980).
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  7. Template:Cite web