Social and cultural training leaves its mark on us. Many new to polyamory will feel some discomfort with some aspects of a non-monogamous lifestyle, but their desire to pursue something less traditional overshadows this in time.
But what about those that don’t choose an alternative lifestyle? No, I don’t mean those coerced, as this is not a part of polyamory. I mean those relatives (and possibly friends) who watch people close to them leave behind tradition and “normal” expectations behind with disapproval and possible scorn?
For some reason, many parents, grandparents, etc are somehow offended and become angry upon finding out that their loved one is breaking with the tradition that they chose for their own lives (assuming that it was not merely assumed, which is often the case). For the most part, this is mere insecurity, close-mindedness, and fear. But there is a legitimate slice of this type of phenomena as well, and that is the unfortunate fact that being polyamorous can be an obstacle towards certain goals, and it is these obstacles that becomes the rub for family and friends.
Especially when conservative religion becomes involved (but certainly not only conservativeness or religiosity), there are many aspects to society that will ostracize and otherwise exclude those that are willing to follow a different path. That is, those with the courage to follow their ideals are squashed for standing out. Why? Well there are too many reasons to list exhaustively, but much of it is not wanting to be associated with the abnormal; being social creatures, people tend to desire fitting in.
And over time, certain abnormal things will become more normal. Interracial dating/marriage was abnormal in much of society in many places and for many years, but now is common. There will hopefully be a day when three, four, or more people in a legally-recognized relationship will not be an example of the result of a slippery slope argument used to scare people from allowing gay marriage.
But before this happens we will need brave people willing to stand in the open in their non-traditional lifestyles and risk the fray. I am willing to be one of those people, and I hope that all of those around me will some day feel the same.
But in the now, there will be the balancing act of how much you allow your family and friends see. There will be those that you trust who will know, and those that you don’t trust. It’s unfortunate, but it happens to atheists too; some of the family you see around their holidays don’t know you reject their religion (or at least lack belief in their god). The real shame of it is that the only way that these things change is through exposure to those that are afraid of change, but doing so comes at personal cost often.
Social good in the long-run at personal cost; a tough struggle.
Skepticism, Properly Applied 
shaunphilly: You can practice all the polyamory you desire.
But just keep in mind that in a society where there is a code of decency observed by the majority, even though a number of such people might transgress at times or even habitually in some acts against that code, behind their facade of decency, the majority is not going to like you for showing gross disregard toward their sense of decency.
And no matter that some of them do act contrary to their code of decency outside of the public view, they still do care to guard their children from the presence of people who do openly flaunt their disregard of the majority’s code of decency.
Gerry
I am not concerned with the fear and insecurity-based codes of the majority. This sounds like the argument that gay marriage threatens “traditional marriage,” which is absurd. How does my being polyamorous directly effect the relationships of the majority? The only way it could is if a “normal” couple, in discovering polyamory, would find that one found it a compelling lifestyle while the other didn’t. But had they not been so ignorant of this basic relationship choice, due to the majority’s code suppressing this possibility (not intentionally, it’s just not discussed because it bothers people), then they may have not created a relationship with one-another and may have found a better match.
This idea of openly flaunting a lifestyle is simply offensive. Why do so many have to flaunt their monogamy? Why do people have to flaunt their religion? Polyamory (homosexuality as well) only looks like flaunting because it challenges the majority. Frankly, the majority should have already challenged itself. Its inability to do so has put them in a situation where the slightest difference in their culture may offend them. That’s pathetic.
The majority does not get to decide what the only way to live correctly is. They can choose to live their lives as they want, but they cannot tell everyone that they have to conform or hide. That would be like telling the minority religions that they can worship their gods, but they can’t let any of the Christians see them otherwise the Christians might get upset.
finding the balance of self-acceptance and societal acceptance is indeed a tough struggle. the path of righteousness is different for each individual; polyamory isn’t right for everyone and in the same vein it’s very unfair that monogamy should automatically be the only legal option for family status in a country that is among the so-called “freest” in the world. changing the status quo is always a lonely endeavour. i’m game!