[...] Claude Meillassoux [suggests] that [incest taboos] were instituted "when control over marriages became one of the elements of political power. [...] In other words incest is a moral notion produced by an ideology which is tied to the extension of power in domestic communities, as one of the means used to control the mechanisms of reproduction. It is not an innate proscription, (if it were it would in fact be the only one of its kind)." Meillassoux concludes by proclaiming that "what is presented as a sin against nature is in fact only a sin against authority."- Arthur P. Wolf, Incest Avoidance and the Incest Taboos
[...] [Meillassoux's theory's] value lies in suggesting that whatever may be the reason for their existence, the incest taboos may have been used to organize or control people. In other words, they may have been co-opted for purposes they were not created for and possibly extended or modified in ways that belie their origins. I will argue later that this helps explain why the incest taboos vary from society to society and why they are sometimes deliberately violated.
[...] Incest is no longer a crime in many European countries, but this is a recent development peculiar to governments whose legitimacy rests on grounds other than moral superiority or supernatural status. Political history tells us that elites almost always criminalized incest as part of the process by which they institutionalized their power.
The twelfth-century Hittites provide a vivid example. Hittite law tolerated couplings between persons related by marriage [...], but prohibited on pain of death couplings between blood relatives. [...] The Hittite concern is preserved in a rebuke issued by Suppiluliuma I to a vassal who was rumored to tolerate sex between cousins and perhaps even between siblings. It reads: "For Hatti it is an important custom that a brother does not have sex with his sister or female cousin. It is not permitted. Whoever commits such an act is put to death. But your land is barbaric, for there a man regularly has sex with his sister or cousin. [...] But you must not desire to have sex with her. It is not permitted, and people are put to death as a result of that act. [...]"
The Roman state was no more tolerant of incest than the Hittite. According to Percy Corbett, the punishment for incest during the Republic was to throw the offender from the Tarpeian Rock, it being "a familiar school of controversy in the first century of the Empire whether a woman who survived the fall should be thrown again." [...] Corbett notes that believing the frequency of incestuous marriages was on the rise in Osroene and Mesopotamia, "Justinian was driven to repressing them with the threat of death to both parties and their offspring."
In imperial China incest was the only one of the "ten unpardonable offences" that did not involve treason [...]. In Ming and [Qing] times (1368-1912) the punishment was strangulation for persons related in the second and third degrees, and beheading for those related in the first degree. Derk Bodde and Clarence Morris note the case of a man who was "sentenced to 100 blows of the heavy bamboo and three years penal servitude" for sexual relations with the daughter of his fifth-degree younger cousin. Severe as it was, this punishment was later felt to be inadequate and the law was supplemented to add "40 days [in the stocks]."
Japan provides a clear case of how the treatment of incest changes with the creation of a strong central authority. When in the seventh century, before the country was united, the Japanese adopted a version of the Chinese legal code, they did not follow the Chinese in making incest an "unpardonable offence," instead leaving punishment of incest to supernatural agents. But when they revised their code in the seventeenth century, after hegemonic rule had been firmly established, they included the Chinese proscription, making beheading followed by public display the punishment for incest.
Politicization of the incest taboos is even more obvious in the case of the Inca. Garcilaso de la Vega informed the world that "it must be known that Kings Ynca, from the first, established it as a very stringent law and custom that the heir to the kingdom should marry his eldest sister." [...] But while requiring that the royal line be perpetuated by way of incest, Inca custom commanded that among commoners "no one may marry his sister or his mother or his first cousin, nor aunt, nor niece or female relative or god-mother, under penalty of punishment: their two eyes will be gouged out and they will be cut into quarters and they will be placed on the hills as a reminder and punishment, for only the Inca is to marry his carnal sister, according to law."
[...] A complete account of incest taboos is possible but only if we recognize their political uses. These explain not only why the taboos are extended beyond the nuclear family, but also why they are sometimes deliberately violated. The general point is that while the emotions that motivate the taboos originate in the family, they are like all other human emotions, in that they can be co-opted to serve political purposes.
Enforcement of the taboo has long been a tool used to increase the perception of the legitimacy of the state. It's no different than how political and religious leaders in African countries and Russia have been using homosexuals as a "foreign" scape goat to rally support behind themselves and gain followers.