They probably didn't have intolerant idiots telling them who they could mate with, either.
Taboos against inbreeding are hardly the result of intolerance since inbreeding drastically increases the probability of recessive genes becoming expressed. Since recessive genes are rarely expressed they're not exposed to the same selection pressure and tend to be less fit as a result.
So your claim is that by engaging in inbreeding, we are putting evolutionary pressure on the recessive genes, thus removing them from the gene pool, and that this is beneficial?
You are aware that, if you have a single gene for sickle cell anemia, rather than coming down with the disease, you're effectively immune to Malaria, since the blood cells will sickle in the presence of Malaria, but not otherwise, right?