The very* definition *of murder varies widely. If you define it as killing of any human for any reason, then you’re forbidding self-defense and defense of one’s country. If you’re saying murder is the deliberate killing of another human being without being threatened by that person, you’re anti-death penalty. (Let’s not even get into the abortion debate.)
Cultures definitions of “murder” are as flexible as the definitions of incest. In some cultures, you could kill a slave for any reason at all as long as you compensated the owner. You could kill your wife if you suspected she was unfaithful. You could fight a man to the death if he insulted your honor. Some countries still have a few of these practices.
I’d like to see a cite for this practice. First of all, I can’t imagine the wealthy/nobility selecting poor children to be a wife for their son, since dowry and social position were the primary motivators for most marriages of the upper class. (Why would a noble mix his blood with a peasant?) Secondly, what the hell does love have to do with marriage? Most marriages of the upperclasses were for dynastic reasons, with no consideration given for the emotions of the two potential spouses. They were expected to do their duty. Thirdly, I can think of dozens of instances where children raised in a communal environment had no problem marrying. (What about Native Americans who lived in large communal lodges?)
And to comment on the Good Egg/Lissa debate, part of the issue is that we need a working criterion of what makes something “just wrong”. The concept of malum de se, “evil unto itself”, is not as clear cut or obvious as some people would think.
something called “incest”, to take an example, even when consensual is a crime/taboo in all societies… HOWEVER, societies vary in what is it that they DO refer to as “incest”, and for half the world (or more) there’s no squick factor in banging your first cousin if she’s game. So THAT is not “just wrong” from some sort of privileged frame-of-reference, it’s “wrong” from a sociocultural or individual psychological or moral angle.
So, in any case, back to the OP, my speculation is that indeed a majority of the population would NOT go ape wild. But boy would there be a whole lot more porn, the Web may grind to a halt However as mentioned earlier, the idea that “if it gets you off, then it’s OK” would be an unworkable scenario; you would have to limit the sexual free-for-all to specifically sexual contexts, lest you make anything OK as long as there’s sex in it (“masturbate while robbing banks” – Heh ) or create a climate of impending rape that actually chills your range of freedom.
Lissa, Der Trihs doesn’t have it exactly right, but not exactly wrong either. It was never the custom for specifically rich families to adopt a future daughter-in-law (tongyangxi); the custom was spread throughout the classes. The practice (according to Wanting a Daughter, Needing a Son by Kay Ann Johnson, a book which can provide a significantly deeper understanding to the history that underlies the current state of affairs in China that has resulted in people like me becoming parents to girls born across the world) was common in the 19th century. It had the advantages of avoiding “the often ruinously expensive ritual costs associated with a ‘normal marriage’, including a bridal price, but they were also able to raise their own daughter-in-law to assure her loyalty and integration into the patrilineal family.”
The Pinker reference actually is not in The Blank Slate, but in his earlier book How The Mind Works p 459, “When the couple grew up they found each other unsexy, and compared to convential couples, their marriages were unhappy, unfaithful, unfecund, and short.” He does not reference that claim. But he also points out that a similar situation has existed in Lebanon where patrilineal cousins grow up together and are encouraged to marry have similarly disasterous results and that Israeli kibbitzim had a similar problem in that kids raised communally often had little romantic interest in each other despite parents often trying to get them to marry within the kibbutz community.
As to the rest of this thread … it has been said well. Some things people wouldn’t do because few people want to do them. Some of our codes exist to explain the ick factor that is hard-wired in there, to explain the behavior, rather than being the cause of the behavior. Obviously behaviors that violate other non-sexual codes are not okay just because they involve sex. Those codes are the basis of society. removal all societal codes and you have no society. Remove all codes involving sex between consensual adults and the odds are you see very little different than what you see now. IMHO.
Because too much of the same thing bores people to tears. Or, as I like to say it, “Name your favorite foodstuff. Then force yourself to eat it exclusively for every meal. See how quick it’ll be before you’re sick and tired of the damn thing.”
People (at least in the USA) get all worked up about sex because much if it is considered taboo by our outdated puritanical standards. Remove the taboo and you remove much of the allure.
However as mentioned earlier, the idea that “if it gets you off, then it’s OK” would be an unworkable scenario; you would have to limit the sexual free-for-all to specifically sexual contexts, lest you make anything OK as long as there’s sex in it (“masturbate while robbing banks” – Heh 
) or create a climate of impending rape that actually chills your range of freedom.