Just so we’re all on the same page, California’s law banning incest doesn’t violate due process rights.
And even if it did, Daniel McEvoy would still be in trouble. McEvoy had sex with his adult sister. They both agree that it happened. Their versions of how it happened differ. She says that she was not a willing participant. He claims otherwise.
The sister, described as Jane Doe throughout the opinion, told her husband about the incident, and he reported McEvoy to the police. McEvoy was charged, and a jury found him guilty of incest and simple assault, a lesser offense under one of the charged counts.
California Penal Code Section 285 criminalizes incest between parents and children, ancestors and descendants, full siblings, half siblings, uncles and nieces and aunts and nephews. On appeal, McEvoy argued that the incest law violated his right to liberty under the due process clause of the Fourteenth Amendment by criminalizing consensual sexual activity between adults.
His argument was based on Lawrence v. Texas, the Supreme Court case that struck down a Texas statute prohibiting "deviate sexual intercourse with another individual of the same sex."
Incest laws are a common -- albeit not universal -- restriction on sexual relationships in the U.S. According to "Privacy Rights in a Post Lawrence World: Responses to Lawrence v. Texas: Is Incest Next?" a law review article sited the appellate court's decision, sibling incest is prohibited in 46 of the 50 states in this country; parent/child incest is prohibited in 47 states and uncle/niece and aunt/nephew incest is prohibited in 41 states. Only 8 of 14 states criminalize first cousin incest.
While popular opinion seems to be that incest is icky (and biologically, a bad idea), McEvoy drew upon the Lawrence court's "refusal to view majoritarian moral views as a sufficient basis for defining a criminal law" to argue that there is no more justification for criminalizing consensual adult incestuous conduct than there is for criminalizing consensual adult homosexual conduct.
A California appellate court, however, explicitly rejected that line of reasoning in People v. Scott. Finding that California's interests in protecting the integrity of the family unit and protecting against inbreeding are sufficiently important to justify Section 285's incest prohibition, the appellate court affirmed McEvoy's incest conviction.