The main reason he gives here is that incest breaks the conservative view of what a family should be, which "violates the natural order" and "messes up the kids". But any first year anthropology course will teach you that there are and have been many, many functional systems of kinship relations and family units that are significantly different from the "mom, dad, kids" structure this article claims is natural and necessary. Is there evidence that children raised in an environment where incestuous relationships occur are "messed up" and "disoriented" like this article is claiming?
I AM an anthropology grad student, and one of the first things we learned is that virutally every human culture has some sort of incest taboo (though as has already been established, what is designated as "incest" varies from one culture to another. I.E. for some cultures cousins are considered incest, in other cultures they aren't). And incest taboos against IMMEDIATE family members are pretty universal, especially when it comes to parent/child relationships. Obviously there are exceptions, but taboos against incest with immediate family, especially between children and parents, are simply one of the most universal social rules in human civilization.
And in general, people in positions of authority are not allowed to enter into sexual relationships with people they are in positions of authority over because it is too easy to manipulate the person they hold authority over. A doctor can't have sex with their patient. A professor can't have sex with their student. And likewise, a parent can't have sex with their child, even an adult child, because even as adults parents are in positions of authority over, and has been stated before, there is such as an inherent risk of adults grooming their children for such a relationship while still developing minors.
So obviously, birth defects for potential offspring are a major concern when it comes to incest laws, but the general rules we have against authority figures being able to date/have sex with people they have authority over also come into play.
From a legal perspective, I imagine the argument is that even though a patient and doctor, a child and parent, etc, CAN possibly have a relationship which is truly consentual and not influenced by the authority figure's position of power, the risk of abuse/manipulation is great enough that whoever instilled the rules/laws concerning such relationships have decided it's more important to protect potential victims than to protect the rights of people who genuinely enter into such relationships without any sort of abuse of power. I'm not a legal person, so I don't know for sure, but that's just my guess.
