Did you know that the actual risk of first cousin marriage is very low? Geneticists have been trying to counter this largely American myth for a long time.

Yes, there is some possibility of genetic “unmasking” of harmful recessive traits with first cousin marriage, but the risk is much, much lower than most Americans assume it is.

Many other behaviors we routinely engage in are much riskier for our offspring than first cousin marriage. And no one would suggest we stop engaging in them.

https://daily.jstor.org/the-genetics-of-cousin-marriage/