I’m surprised that nobody has ever tried to change the species so that “having a pure bloodline” doesn’t result in the offspring being deformed or stupid. I’m not defending that kind of thing, but maybe royal families (if any still exist in this current day and age) who are obsessed with keeping their bloodline “pure” would one day realize that such a task is impossible, and the only way to come close to that “ideal” is by changing the species.
I don’t think human genetic engineering is legal yet.
Regardless, all species* are suseptible to the drawbacks of inbreeding; it isn’t just a Homo sapiens issue.
*Just look at cheetahs, for instance.