Midwives have been told about the benefits of “close relative marriage” in training documents that minimise the risks to couples’ children.
The documents claim “85 to 90 per cent of cousin couples do not have affected children” and warn staff that “close relative marriage is often stigmatised in England”, adding claims that “the associated genetic risks have been exaggerated”.
It also compounds over generations; if you’re the child of first cousins, you really should seek someone who it would take genealogy research to find a common ancestor with. If you’re not, it’s still a serious risk to have kids with anyone too closely related, but level ramifications seem really harsh, especially thinking of situations like adoption where someone could end up there accidentally. And to your point, it isn’t the only way to end up with that kind of risk profile.
Good thing that it’s possible for a couple to take a test that gives a good measure of their degree of consanguinity.
This is a particular risk not only in countries with first-cousin marriage, but in those with small founder populations. For example, Iceland, where the government provides this measure to any couple who asks, so that they can make an informed decision about the risk before reproducing.
And ethno-nationalists can choke on this fact: the best strategy to reduce the risk of genetic defects is out-marriage. The less closely genetically similar two partners are, the lower the odds of autosomal recessive disorders afflicting their offspring. So I did the rational thing, and married someone whose ancestors came from a different part of the world than mine.