Should incest between consenting adults be a crime?

[Angrboda]

Should incest between consenting adults be a crime?

This came up in my reading and seemed like a good topic.  I haven't formed any conclusions one way or another, but would like to solicit opinions.  The article notes that there are places where it is not a crime.  Should it be illegal?  Even if it were not illegal, would you consider it immoral?  Why or why not?

There is an evolutionary reason we don't fuck family members closely genetically related. It is still a "EWE" factor for most humans. 

This may be true, but should it be illegal when there is no possibility of children, such as when the man has had a vasectomy, or the woman infertile? What if they are practicing responsible birth control? Is the "ewe" factor alone enough to justify discouraging or criminalizing otherwise harmless, consensual conduct?

I take it you're referring to the potential for genetically handicapped children to be born. I'll note two things. First, my understanding is that the risk is exaggerated. Second, if we forbid sex for that reason, do we also forbid sex among others who might be promoting genetic abnormalities by having sex, such as parents who both carry the Tay Sachs gene? Once we go down that road, do we allow other justifications for denying people the right to have sex and have children because the consequences in terms of the children's well-being or quality of life are likely to be undesirable? Do we forbid mothers of down syndrome babies to have sex? (I don't offhand know if there is an increased risk for such mothers, but I think you know the type of thing that I mean.) Do we extend such reasons to whether the parents are unintelligent? Do we forbid black people from having sex because a black child is more likely to have a lower quality of life than a white child?

I started this thread with the intent of talking about siblings that are related, and I would like that to be the focus of the discussion, but there is also the issue of criminalizing sex between half-brothers and half-sisters, or even those not genetically related but related through adoption or marriage. I think that represents a separate problem, and people can comment on it if they like, but I think the primary objections are about sex between genetically related siblings, so that's probably the most salient case.

The taboo against incest runs deep, as the social psychologist Jonathan Haidt demonstrated when he told experimental subjects about Julie and Mark, adult siblings who take a holiday together and decide to have sex, just to see what it would be like. In the story, Julie is already on the Pill, but Mark uses a condom, just to be safe. They both enjoy the experience, but decide not to do it again. It remains a secret that brings them even closer.

Haidt then asked his subjects whether it was okay for Julie and Mark to have sex. Most said that it was not, but when Haidt asked them why, they offered reasons that were already excluded by the story—for example, the dangers of inbreeding, or the risk that their relationship would suffer. When Haidt pointed out to his subjects that the reasons they had offered did not apply to the case, they often responded: “I can’t explain it, I just know it’s wrong.” Haidt refers to this as “moral dumbfounding.”

~ Ethics in the Real World: 82 Brief Essays on Things That Matter