@TheWanderer567 Why should they? I guess you have no real idea how incest works? Your kids dont just become abominations just because their parents are siblings, it only raises the chance of a genetic disease/defect. But first the parents need to have a defect in the same gene, with siblings its more likely due the same parents, but it can happen with non-siblings too or not happen with siblings and even then there is only about a 25% chance that the child will have a disease or deformity out of this. The risks are high compared to non related couples, but they are still very low overall.
Even with several generations practising this its absolutly possible that no major disabilities came out of it. (On the other hand, his sister doesnt seem alright in her head)
@BluePanda I wont admit, because im the opposite of that argument, i understand him and his sister has some serious problems...