Also its is becoming common practise for people to have medcial checks done to see of any genetic disorders and I'm not talking Emaratis here. Just because your not related does not mean either one or both are not carrying anything in their DNA.
True, Im not sure but I think in Iran it is even a law that if cousins want to get married they MUST go through medical checks.
As I mentioned earlier, in Islam they are rules and restrictions on relationships even in families.
“Mahrams” (As you might call them immediate relatives are mother, grandmother, daughter, granddaughter, niece, aunts. ( they are some other like mother’s aunts etc etc which I m not going through them here).
Islam restricts relationships with others out of this circle, and as you can see cousins are not in this group. So there cannot be close friendship with cousins like what they have with their siblings, and as culture is affected so much by religion, marrying cousins is just like marrying outsiders.
Abt the benefits ( which I don’t really believe in) rather than cleaning the gene pool, they say as the know the family very well, it can prevent the couple from future problems.