@Tyro - Of course incest is morally permissive. The majority of people in this thread agree with that.
Now, let me ask you this.. How would you feel about a father and a daughter having sex for the sole purpose of having a baby? And for the sake of the question, let's say that they are both aware of the possible negative effects it would have on their future child.
Personally, I haven't worked it out. I saw the word Nazism and my thoughts shifted from concern for the potential offspring to concern for the parents. If incest is disallowed, then where does the line end? And who draws that line? If someone can regulate who I can make a baby with, for the child's sake, could I stop two Jews from procreating so the child doesn't have to suffer through life with a huge nose?