It is one of the forgotten ways that Christianity had this benifit in the West -
the Catholic Church's decision in the 6th Century to ban between first cousin's was one reason why our civillisation started to pull ahead of the rest.
For every 500 years a country was under the influence of the Western Catholic Church there was a 90% reduction in rates among cousins.
A 2025 study showing almost half (46%) of Pakistani mothers in certain Bradford areas were married to a first or second cousin.
The consequences of cousin marriage are-
Deformaties and terminal illness disorders -doubled risk
An average 10 IQ points lower
1/3 birth defected children of Pakistani marriages in the UK at the time only 4% of births.
There's another benifit to not having cousin marriage as well-
If you have to look outside your own family for a match then it makes you less tribal, more trusting of strangers:
...Globally, we show that countries with longer historical exposure to the medieval Western Church or less intensive kinship (e.g. lower rates of cousin marriage) are more individualistic and independent, less conforming and obedient, and more inclined toward trust and cooperation with strangers.(Science Magazine)
If you are only marrying within your own family your society tends to be more insular, more conformist, family elders have more say, a functioning government is less important to you than your 'tribe.'
We have been very lucky to be born into a society without this as a social norm, but with mass migration it has to be re-established that our values and norms are better for society, and cousin marriage should not be allowed to flourish here.