The short answer: none—that is, if all that’s required for a morally permissible sexual relationship is that it involve: (1) adult partners; (2) who are mentally competent; and (3) who fully consent to the relationship (for good measure, we could even add that the partners have a sufficient emotional bond and that their sexual acts serve to express that bond).
This is increasingly becoming the standard, of course, for society’s determination of whether a sexual relationship is permissible. It’s for this reason that the lawyer representing the Columbia University Professor, David Epstein, accused of a three-year incestuous relationship with his adult daughter, can sincerely ask, “It’s OK for homosexuals to do whatever they want in their own home—how is this so different?” As such, we should not be surprise that Switzerland is considering legalizing consensual incest between siblings as well as parents and their adult children. Switzerland is not blazing any trails, however, for, according to one study, incest is already legal in China, France, Israel, the Ivory Coast, the Netherlands, Russia, Spain and Turkey (the article citing this study did not clarify, however, whether it’s legal because there’s never been a law against it, or whether an existing law forbidding incest was overturned).
Unfortunately, many who oppose incest, morally, legally or both, reveal that they too accept the fundamental premise that a sexual relationship need only be a consensual relationship between two competent adults. For they object to incest not by denying this premise, but by arguing that such relationships are inherently coercive. Thus, instead of objecting to incest by saying more is required for a morally legitimate sexual relationship, they merely argue that such relationships cannot be fully consensual. Given that it’s not immediately obvious that incest between competent, consenting adults is inherently coercive, absent an admission by one of the persons to that effect, this argument doesn’t appear to have much promise in preventing the legalization of incest.
Of course, some may add that there is also the social taboo and “ick factor,” which points to the fact that incest is something we just know is wrong deep down in our gut. Assuming our sensibilities are right, and I think along with most of our society that they are, that means we must reject the assumption that sex is ok so long as it’s between competent, consenting adults. For, even a mediocre student of logic knows that this assumption can’t be right if it leads to the absurd result that incest is permissible. But note: if we reject this assumption homosexual sex can’t be moral either, not to mention pre-marital heterosexual sex.
While I’d be glad to end the argument here, the problem is we can’t rely on social taboo or the “ick factor” regarding incest any more than we might have with respect to homosexual sex. As we’ve seen with the change in social attitudes toward homosexual unions, our sensibilities can be easily eroded through social pressures toward tolerance, acceptance and understanding, not to mention steady media bombardment. Perhaps it won’t be long before NPR’s daily dose of stories about the suffering and heroism of homosexuals will turn to similar stories about the suffering that a father and his daughter, a mother and her son, or a brother and his sister are experiencing because society refuses to accept that their erotic love for each other is legitimate, if not perhaps even beautiful. Thus, unless we’re ready to embrace what awaits us at the end of the road, a road down which we are already heading with increasing speed, we need to articulate and hold fast to the moral foundation that explains the social taboo against incest and justifies our gut reaction that it’s repugnant (an effort I will make in a second post).
Books on the topic of this essay may be found in The Imaginative Conservative Bookstore.