Did you know Rhode Island exempts Jews from its law barring Uncle-Niece incest and marriages? This is to allow Jews to fulfill certain commandments laid out in Leviticus. While Jews no longer condone Uncle-Niece incest (centuries-old Talmudic interpretation has essentially nullified the doctrine entirely), it does kind of give lie to cheap talk about "a code of conduct stretching back to Sinai" being against incest. There's a weird tendency among some authors to assume that "bad things" are exactly interchangable with "things the Bible condemns." It's not true, and often times it leads to really sloppy writing. Not to mention, an atrophy of critical thinking on our part as to why we think Uncle-Niece incest is wrong. As this case demonstrates, always deferring to our ancestry can lead to some dangerous and unforeseen commitments.
The Rhode Island law isn't exactly an anomaly, either, though its the only one to single out Jews. Several other states have exceptions to Uncle-Niece incest and marriage laws (Minnesota and Colorado permit it for "aboriginal cultures"), and Oregon doesn't bar Uncle-Niece incest at all (though it does not recognize marriages). I suspect most of these laws are relics of some form--I doubt any would pass today. It's just an interesting legal and historical note that I never knew.
It certainly would make for an interesting case example for my paper on Jews and American Church/State relations, though.