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”.
Plus in the absence of any power dynamic* why shouldn’t absolutely anyone be allowed to choose to be in a relationship with literally anyone else? Especially as people are increasingly choosing to not reproduce.
* If this is even possible
Usually the argument goes into the ethics of bearing children in a way that, knowingly, creates a significantly and markedly higher risk for every kind of disorder reducing the child’s QOL. I don’t usually find this argument anywhere near airtight, since there’s a plethora of other ways to do that that aren’t banned AND this veers into eugenics territory. But that’s the argument I’ve seen, at least.