I can't really see a justification for the ban of two adults consenting to sex, who just happen to be blood related. This isn't a subject I get passionate about or anything, but I really can't think of a good enough reason as to why incest should be banned.
Your opinion on the act being disgusting isn't good enough to me. You may find beetroot disgusting, but that doesn't justify banning it. The (slightly) increased risk of the children being born with abnormalities? So many genetic diseases out there are passed on with no opposition whatsoever. Family trees with a lineage of miscarriages from the mothers does happen. HIV? Cancer? All those are somehow passable, but incest? Nah, we'll ban that based on our subjective view that it's disgusting and gross.