The biggest argument against incest is the fact that it makes it more likely you will inherit recessive genetic diseases. This argument, morally, is false because then we would need to stop women over 40 from having children as this also increases the chances of internal disease. What is the point of incest? What is the point of incest in animal breeding? The point of incest in animal breeding is to bring together clusters of genes which could only be accomplished through incest. After several generations of amplifying a set of certain genes, you have a standard breed of dog or horse with predictable physical and behavioral outcomes. If applied to human families, standard breeding of humans could be produced.
What is the point of creating standard breeds of humans? I come from the eugenic philosophy of Beyondism (here) which asks us to understand that it is very hard to predict which characteristics in humans will be best suited to the future and it is very hard to determine which morals we should use. Beyondism prescribes that the human race break up into ethno-states so that each nation is a cluster of related genes. Then we allow these ethno-states to form their own cultures. Genes and cultures are observed and those that are deemed helpful are absorbed by other member ethno-states. This is what Beyondism calls "cooperative competition", the differences between nations are measured and the best genes and culture are inducted. Obviously, those genes and cultures deemed deleterious are rejected and bred out, and culturally extinguished.
What does this have to do with incest? It would be much easier to create isolated cultures and genes which are extremely honed and different from other groups through incest than it would be to take from several nations based on Beyondism principles, family culture of Beyondism instead. Genes can be isolated by families and family culture can be used instead of national culture. This Beyondism on a small scale would be much more practical today than intertwining Beyondism into the state.
But still, there is the problem of genetic mutations and also the problem that families might not be sexually attracted to each other. But today we have science. We are able to screen embryos for genetic disease. We can also impregnate without sex so this eliminates the problem of unwanted sexual contact. Specific genes can be combined again through genetic screening and artificial fertilization. Science will make all the problems associated with incest eliminated, science is an ally to eugenic incest.