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”.
On the other hand, you can have marriage without children and children without marriage.
Unless you start punishing them for having children, it’s naive to ban marriage.