For some reason it seems to me that many people have missed what the OP's original intent was. This was not meant to be a discussion exploring whether incest is morally right or morally wrong, the OP and everyone can agree, that for the most part and in most instances, incest is morally wrong. No one has argued for incest, some of us have just said that arguably not all instances of what can technically be considered incest are the same and so there may be subtle shades of gray.

What the OP wanted to explore was what creates the "ick" factor about incest from an objective standpoint? If you separate out the, "because it's bad" automatic response, how does one justify the repulsion to incest? (Yes we all know that incest destroys the family unit, that again, is a given.)

Madame R suggested that incest produces the "ick" for her because you don't want to be with someone who farts on your head. I suggested that the incest produces the "ick" for me because my emotional needs and feelings of intimacy are satisfied from my family, so I have no need or desire to see them in any other way. I think many of the people who are expressing fantasies of incest are doing so because they lacked the emotional connection to their family members and they are attempting to relive family moments with stronger expressions of love--it's distorted but emotionally starved people sometimes make emotionally immature decisions.

I'm not sure if it's possible for people to discuss this issue objectively, the immediate response of "because it's bad" is a bit too easy and common. The issue is whether you can express your "ick" response in an objective way? As someone stated, at one point, inter-marrying was considered acceptable. What prevented those families from having the "ick" factor?

Personally I'm not interested in understanding this debate, I don't need to. But I read the OP's thread and appreciated that he was attempting to explore an intellectual discussion about what is behind the "ick". This would be akin to someone asking a gay guy why he thinks a woman's vagina is "icky" or a straight guy why having anal is "icky". I think it's good for people to understand what really motivates their opposition to things so they have a greater understanding of the issue beyond a knee-jerk response.