Just because two adults consent to an incestuous relationship,
it doesn’t make it right. God, with his
limitless wisdom, outlawed incest. This
was not only because many underage children are victimized. It was also because incest is disgusting. With all of the eligible mates available in
the world, why would someone want to date a family member?
First a family born out of incest increases the rate of birth defects and mental retardation. This gets worse with time if there is a tradition of incest. If your parents are cousins whose parents were cousins and marry your own cousin, well that's going to lead to a very unhealthy (biologically speaking) offspring. This can be seen in small communities that only marry within their community even if the don't marry family directly. : http://www.ibtimes.co.uk/amish-gene-mutation-mental-retardation-developmental-delay-445578
Also most types of inbreeding usually are due to an unhealthy relationship within a family. Cousin-Cousin marriage isn't as bad as parent-child or sibling relationships biologically but it leads to peculiar societal traits. In countries that practice this as well as FBD or Father's Brother's Daughter marriages there is a behavioral tendency to become "clanish." Like Afghanistan or Scotland used to be before modern times. This leads to corruption and a lot of fighting with none-relatives. Often women are mistreated in these societies.
In the single one off cases it is often an inappropriate relationship between an older relative taking advantage of a younger one, so there is always a power imbalance in the relationship.
So in short don't do it! It harms your family or the family that results from it. We have a mechanism where we do not find people we grow up with attractive as a barrier to incestual relationships.
I meant to thumb down but I hope my point comes across. DON"T DO IT!!!!
No, I do not think that adult incest is consistent with the family unit and should always be banned. I think that adult incest, or incest at any age, destroys the family unit and creates a biological structure that just isn't right. At any age and any time in life incest should be banned.