Now why can't MY controversial threads be this entertaining and civil? After reading through most of all this, I figured I'll add my own alien perspective in on it.
I've always divided the sexual morality people into 2 groups:
1) Those who cannot relate to the variants
2) Those who judge by the book
In the former, its the people who are 100% straight/monogamous and cannot FEEL anything about those who are not; they don't necessarily hate, they just don't get it. The latter are the people who base their value system on the protocols...they rail against homosexuals or see them as bad because they're obligated to according to the "rules" (e.g. The Bible). I often wonder how those in #2 manage to be so malleable as to be able to let an outside source determine their every choice: they literally filter their feelings and develop reactions through an artificially implanted sieve. Of course, since this "sieve" is built of unquestionable fiber (i.e. "God's Will/Word is Law"), they never question it...if they feel anything contradicting it inside, they suppress it or attempt to re-educate themselves. And this is where I get started...
Like many of my own threads have stated before, I figure most of the issue is based on perspective, which is usually affected by invisible or subliminal influences that we largely aren't aware of, and tend to defend rather vigorously (you might say that was one factor in the failed circumcision thread). So when it comes to the concept of polyamory, you have to stand WAY THE HELL back and examine the oldest or most distant parts of the concept.
Human societies don't exist in a vacuum: they tend to influence each other in the moment and those experiences/memories influence those who come later. It's the way packs become communities and how communities become civic collective; its a telescoping effect built on standardized practices and shared information over time. And just as prostitution might be the world's oldest profession, so too might marriage be the oldest institution, and so as a result, you have several thousand years worth of collected ideas cross-pollinating and combining and evolving with trends, revolutions, cultural shifts, and even environmental changes.
For purposes of this discussion, we're talking about love. And most of the attitudes coming up tend to be based on Variant Indo-European Union Architecture and Abrahamic Sexual Morality. Both of these influences have a distance of about 2,000 years apart, so maybe this can account for double-standardization that we might see.
VI-EUA is the younger model, based on modified Abrahamic codes cross-pollinated with pagan European cultural models. The Post-Roman world underwent a complete renovation and gutting of the old practices in order to replace them with the "newer, better" Christian ways...one reason i think Christianity took hold so well is the central conceit that the Final Message had been delivered by Jesus and that invigorated the already imperialist Romanized cultures still behind...the whole "waiting for the Messiah" humility of the Jews probably didn't resonate very well with aristocracy. So with the pantheons, the Antiquity Age philosophies went with it, and the extended musings of the Greeks, the Romans, and others--ironically, it was the Arabs and later the Muslims who would inherit and protect these ideologies, only to reject them centuries later--were replaced with the absolutism of the Judeo-Christian morality system.
The Greeks had many different notions of love--most of them now illegal--but they had about as many different names for love as Eskimos do for snow. It was not a fixed concept, whereas in the Abrahamic tradition, it becomes one, and a concept mutually tied to obligatory behavior: "love", as it is in the Jewish tradition, is more of an act of obedience than of personal satisfaction, and if you raise a person to associate happiness with pleasing others, then they can interpret happiness reactively rather than subjectively...basing their feelings on the approval/disapproval of others.
Incidentally, this is similar to how abused children can interpret a punch in the face or rape as a sign of affection: act on it and reinforce a perception about it and you can make someone love what they hate.
With this in mind, you didn't have to believe, because you could gain benefits just by doing--what Queen Victoria would later summarize in her famous phrase "Lie back and think of England"--and a long history of hypocritical behavior by popes and potentates pervaded until the various revolutions later evolved and resisted them. But even these resistances based themselves on the older Abrahamic template...they didn't abandon it, they just eliminated the aristocratic notions. So what you have is a palimpset: a collection of conflicting ancient cultural practices with radical reactionist philosophies and the result is a mess of "why do we do that?" That continues today.
Abrahamic Sexual Morality (i.e. the moral defenses/oppositions to sexual practices) are based on Jewish Sexual Laws, which are a form of property management. The Abrahamic religions (Judaism, Islam, Christianity) and their cultures are all based on a nomadic desert tribal culture, where strict unanimity and resource distribution are the central tenets of group survival; any variation or exemption can cause disastrous disarray because of the fluctuating nature of life quality--the changing state of resources (water, game, shelter, etc.) kept them from forming the specialized departments/ministries of governance that are made to handle variances in lifestyles--and therefore required violent rehabilitation to keep people in line. It would make sense that a people at the mercy of the harsh elements would adopt/believe in a deity with a similar temperament and emphasis on group conformity. And if this deity (YHWH/Elohim, Jehovah, Allah) were the central authority, then the moral, cultural, infrastructural (etc.) protocols of the culture would be attributed to Him and His will (i.e. values/perceptions) would mirror the community as well. And they would thus be considered obligatory and intractable.
So, since this is a culture living a hardscrabble existence in an increasingly agrarian--and soon to be industrialized--polytheistic world, life becomes an endless series of mortal threats...and so childbearing becomes an almost obsessive and even mandated concern for the group, especially if your infant mortality rate is as high as it was. Combine that with rampant xenophobia--which would happen to any isolated group surrounded by larger, stronger, centralized communities--and you then have a concept of purity, and ethnic obligation, as well as filial piety. So, the people in the community would, in turn develop concepts/perceptions of pair bonding that MATCH the collective (read: Divine) value system.
Basic psychology: individuals in a group assimilate into a whole unit (mob mentality). So, convince an individual to associate self-identity with the larger group and their value system will evolve to synchronize.
So the Abrahamic Sexual Laws are utilized because they were a way of ensuring a sole line of blood lineage, in order to determine the inheritance of the resources and authority in the family. If a woman breeds with another man, or a man impregnates another women, then you have a division of family, and then a division of resources...this could be disastrous when determining who would be next in line for any leadership positions. In fact, we have the same legal concerns today: think of how many fights, disputes, kidnappings, and murders have occurred over disputes with half-siblings and second wives/husbands concerning matters of inheritance or estate...maybe it's always been that way. But because Abrahamic laws are bound to religious foundation, and because religious value systems are based on dichotomies of absolutes (EVIL/GOOD), the variations of lifestyle become interpreted along those lines. Hence, why homosexuals are always attacked by religious groups.
ALL THIS is the basis for how our culture formed: we formed into a progressive egalitarian variant of an Abrahamic culture...and that's a problem because the 2 are TOTALLY INCOMPATIBLE, although it would take a few centuries for those discrepancies to reach a mass critical enough to observe.
Most other cultures that adopt this modernist approach are ABSTENTIONIST cultures: if it doesn't endanger lives, the government, or personal safety, then it's none of the government's business. Abrahamic cultures and those influenced by them (America) are INTERVENTIONIST cultures: like their nomadic forebears, certain behavior is WRONG REGARDLESS OF ANY OTHER OTHER CONSIDERATION AND MUST BE ACTIVELY STOPPED...or "society will collapse!"
So since these influences have been given to us our entire lives, we tend to form reactionary opinions to certain issue without thinking about them...and when we do, we tend to side towards the ones that make us comfortable (i.e. familiar). So it's one thing to think about polyamory as wrong because of your conclusions on biology/evolution or based on your own personal inability to relate to it...but its another to have the same attitude because SOMEONE ELSE TAUGHT YOU TO THINK THAT WAY.
In that case, your opinion was contaminated...you never developed it on your own. You didn't research it, examine it, study it, interview practitioners, collect data and form an informed opinion, you just borrowed or recited what someone else imprinted in you; studies have also shown that the human brain is designed to receive a small chemical high and actively seek out information that reinforces a personal belief system, but WHERE DID THAT BELIEF/VALUE system come from? Did it emerge preternaturally from inside or did it get positively/negatively reinforced by others?
So, based on my attempts to form an opinion based on cause-effect rather than influence, I see no logical reason to think of polyamory as anything detrimental to human relationships. There is no definite proof that humans are naturally monogamous or polyamorous (in fact, given the genetic differentiations--e.g. race--in humans, it possible that there are different reproductive programs in humans). Like all relationships, it carries with it a certain amount of structural and psychological complications and benefits, and therefore requires a balance of properly calibrated personalities and chemistry to work. The tendency towards monogamy or polyamory is LIKELY--not proven--to be a personality-driven characteristic more than socially enforced, although external influences can nourish/atrophy in either direction.
Polyamoroy has its own structural integrity requirements...and if those requirements are met, then there's no reason it cannot function as an efficient system.
)). 
. But really, that goes back to insecurity; it stems from not getting what you need. I get what I need and I'm satisfied and deeply loved. 
