first cousin marriage largely illegal in the US
https://en.wikipedia.org/wiki/Cousin_marriage_law_in_the_United_States
inbreeding and IQ
https://www.sciencedirect.com/science/article/pii/S0160289608001608
So marrying your sister would be even better right? The Muslims are selling the Euro weenies the rope they will hang themselves with.
I had clients who were half siblings. They couldn’t understand why their children were low IQ, had physical disabilities and a couple died. Oh, but they loooved each other, sigh.