Look, in the modern age, this law is about as close as we can ethically get to eugenics since most people would agree that incest is immoral. Mixing genes that are so closely related can lead to birth defects and is generally not very good for genetic diversity. As for JRwakebord's remark about the guarantee of infertility: I guess an incestuous marriage could always include castration as part of the ritual.

Il papa caca nei legno?