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.")