Interestingly enough, only about half of the States prohibit the practice. Both Virginia and the District of Columbia permit it.
So, when Montgomery County housing-code inspectors investigate reports of massive home overcrowding, but can't take any action because all of the residents claim to be related, and they remark after observing the many offspring of people who claim to be close relative, "so incest and inbreeding are part of your Cultural Diversity?", now the imported inbreds can truthfully say "Absolutely, and it's part of yours as well. There is no law against it".
Other than the laws of nature, that is.

Which might tend to explain all of the good-looking criminals and highly-attractive sociopaths that flourish in the region, as well as a lot of folks so fireplug butt ugly that you know that the only reason they were born was because the family fixed up some cousins to get hitched so they wouldn't die alone. I can just imagine the conversation, "It doesn't matter how ugly they are, they're a relative, and even your first cousin needs love too, even if they have no forehead and their ass flaps when they waddle. And with your crossed eyes and mono-brow, not to mention the flatulence and webbed toes, who else would have you?"
Well, it's well known in the pet-breeding community of the "Cat Fancy" that aside from obvious things like hip-dysplasia, inbreeding also frequently affects temperament.
I've been endlessly asking "how is it that we, as a society, have become so batshit crazy?" -and the simplest answer is that society is as inbred as a Siamese Cat.