>>717442591They don't really have one outside the visceral disgust reaction society has instilled in them.
The genetic risk is lower than the mother being over 30.
The westermark effect doesn't actually exist. And even in the study that "discovered" it, only showed up in the girls.
The IQ destruction claimed to cosanguinous relationships is more readily attributed to the pre-existant inferior genetic stock of the populations that still practice it than an actual deleterious effect. The randomness of regression to the mean is more deleterious of IQ
The absolute, base line reason society is against it is the power clans used to wield in the feudal days. It was a third branch of power balancing out the full nobility and the church. So the state and church conspired to destroy these large blood-related organizations and their ability to hold onto and shepherd wealth.
And we see that continuing into the modern day. Though the state has also turned on the church now. But the continuing atomization of groups down into individuals responsible and loyal only to themselves is the ongoing path of the anti-incest root.