@salt
>While pregnancies from sex between first cousins do carry a small risk of birth defects, this risk is often exaggerated:[406] The risk is 5–6% (similar to that of a 40-year-old woman giving birth),[406][407] compared with a baseline risk of 3–4%.[407]
https://en.wikipedia.org/wiki/List_of_common_misconceptions#Human_sexuality
We ban based cousin marriage but not hags breeding, why? That's not including any social problems either