In my last post I noted, if one wants to justify (the normally prohibited kinds of) incest (as noted, if you extend "incest" beyond the nuclear family, we are all distant cousins), perhaps one could use, NOT same sex marriage but the Bible itself in certain circumstances (though what that Columbia U Prof. did probably doesn't qualify under the exception).
The Bible does in some sense prohibit incest like it prohibits lying and rebellion against government. I used those latter two as examples because there is debate as to just how "absolutely" the Bible prohibits those things. We've all heard "there are no absolutes" to which good, Bible believing non-relativist believers balk. "No, there is truth in black and white".
But even regarding something so elementary as lying, there is an arguable biblical defense of "righteous deception" that accords with the reductio, "would you tell Nazis who knocked on your door whether you were hiding Jews in your attic?"
Likewise with Romans 13, the biblical-Christian case for "rebellion" (if there is one) relies on the idea that the Romans 13 prohibition against rebellion, properly understood, is a general rule that is qualified with exceptions. If an exception does not exist (which some/many biblical Christians claim) then the American Revolution was not a biblically justified act. (What do you value more, the American Founding or the Bible?)
As an attorney, I'm familiar with the common law rule that "necessity is a defense to all crimes against homicide" (likewise with duress). Does the Bible, arguably, teach the same thing on incest? Imagine in the present day a twenty something brother and sister, with drop dead gorgeous good looks/physical appearances stranded via a plane crash on the Island of Eden as a result of a huge calamity which, as far as they know, killed millions of people (perhaps much more, perhaps they are the last two survivors on Earth). Fortuitously (or Providentially), they have what they need on that island to survive.
Now, they may have such a strong incest aversion that the answer is already made for them. But maybe not. What do they do, using the Bible as a guide? There are the general, above linked incest prohibitions. But there is also the Garden of Eden, which, literally interpreted, means all humanity came from two human beings, necessitating either brother and sister or some other kind of incest. There is also, from the literalistic perspective, the story of the 8 humans left after the Noahic flood which likewise necessitates some kind of incestuous reproduction.
Finally, there is the story of Lot and his daughters. I had to reread this one after someone informed me via email that the context of the tale is clearly anti-incest. I'm not so sure.
As the Bible says in Genesis:
31 One day the older daughter said to the younger, “Our father is old, and there is no man around here to give us children—as is the custom all over the earth. 32 Let’s get our father to drink wine and then sleep with him and preserve our family line through our father.”
33 That night they got their father to drink wine, and the older daughter went in and slept with him. He was not aware of it when she lay down or when she got up.
34 The next day the older daughter said to the younger, “Last night I slept with my father. Let’s get him to drink wine again tonight, and you go in and sleep with him so we can preserve our family line through our father.” 35 So they got their father to drink wine that night also, and the younger daughter went in and slept with him. Again he was not aware of it when she lay down or when she got up.
36 So both of Lot’s daughters became pregnant by their father. 37 The older daughter had a son, and she named him Moab[g]; he is the father of the Moabites of today. 38 The younger daughter also had a son, and she named him Ben-Ammi[h]; he is the father of the Ammonites[i] of today.
There are two competing contextual themes here. One, the anti-incest idea that the daughters had to get the father drunk -- therefore, they all knew something was wrong with what they were about to do. Versus, two the necessity in preserving the bloodline, the idea that they felt they had no other choice to fulfill the biblical command to "be fruitful and multiply." And this necessity defense also resonates with the story of the Garden of Eden AND the propagation of the human species after the Noahic flood.
The Bible, seemingly, is precisely the opposite of a "book of absolutes."