Always?  Sometimes?  When?  Why?

Why does the law prohibit incest?  Is it just another example of a deep-seated social convention or a prejudice, like the feeling some people have about gay marriage or polygamy?  Who is hurt by it?

The matter comes up again now as a Columbia University Professor has just been charged with having a three-year sexual relationship with his adult daughter.  Many are outraged by the behavior, but others argue that what adults do consensually with each other is nobody else’s business.  Is it possible to think about it coolly?

A recent piece on Slate tries to marshal the arguments.  The one that has gotten most contemporary attention is genetic:  inbreeding compromises the gene pool and leads to a much higher incidence of birth defects and developmental disorders.  That’s true, but these days the increased technologies of contraception undermine that argument.  From that perspective, “protected” incest would be OK.  And what about same sex incest, where there is no danger of conception?  As Slate put it:  “If both parties are consenting adults and the genetic rationale is bogus, why should the law get involved?”

Ohio’s Supreme Court offered a different rationale:  “A sexual relationship between a parent and child or a stepparent and stepchild is especially destructive to the family unit.” This destructive effect, the court reasoned, occurs even if the sex is adult and consensual, since “parents do not cease being parents … when their minor child reaches the age of majority.”  The argument is that it is confusing and disorienting to everyone in the family. (See, “Incest Is Cancer.”)

That strikes me as a better argument, but, then, what if it isn’t confusing?  What about the special cases where it is precisely what the parties want.  That may be confusing to others, but is that a reason for the law to intervene?  Moreover, there are so many sources of confusion in families today:  divorce, adoption, same sex parents, in vitro fertilization, parents living and working in different cities.  Why single out incest?

Freud argued that the reason we prohibit incest is that we are so powerfully tempted by it.  That’s why it’s taboo, not just illegal.  We have to erect barriers of horror and disgust to prevent ourselves from succumbing to temptation.

That has to be part of the argument.  Children need to be protected from sexual exploitation by parents, because it is all too easy for them to be abused.  Parents are strong and lustful, but children are weak and vulnerable.  And we know all too well the life-long damaging effects on children who are exploited by those on whom they are dependent.  Their capacity to trust others is impaired if not destroyed.

So we need laws and customs and taboos – whatever it takes —  to preserve the trust that children need to have in their caregivers.  That trust is not only the basis for their future relationships with others.  It’s the basis for the confidence they need to be responsible adults and citizens.