OT? (Genetics, sorry....at least I warned you)
I actually looked it up a while back, and was shocked to find many places/doctors support first cousin pairings, including California and the UK. It is apparently mostly a social issue and not so much a genetic issue. (Fun fact, Charles Darwin married his first cousin.) So definitely not a barrier to the blind being true.
In response to other posts, I also read that inbreeding is not as common/severe as people think in EU royals, with the glaring exception of Spain and the resulting "Habsburg jaw" - uncles should never marry their nieces. Can you imagine if that happened in 2022? And even though perfectly legal, if Archie married Charlotte or George married Lilibet, I think the world would still riot.