I have written a lot over the past few years about nonmonogamy - that is, relationships that involve more than two people. I have consistently found that the sort of people that write and talk about polyamory are the same as any fringe group anywhere in that they all have a gripe with mainstream society but the infighting between them is the fiercest of all. For example, poly folks complaining about other poly folk not doing it right. You know there is some real attention getting focused on polyamory because in an article about how Katniss Everdeen should be able to have two boyfriends instead of having to choose between them people complain in the comments about how poly folk are oppressing them and not respecting their monogamy!
There is a big trend towards talking about having more than the standard two people to a relationship but there is just as much of a need to talk about people who aren't in any relationship at all. Both of those types are going against the grain but the perception of them from the outside is quite different. People with more than two in their relationships tend to be seen as hedonists with no self control and people who are single tend to be pitied and regarded as unfortunate or broken. Things go both ways though, as always; poly folk tend to view monogamous types as unevolved, ignorant, or repressed and singles sometimes characterize them as mired in commitment.
All these attitudes suck. Obviously there are a lot of people out there who are desperately searching for their one and only soulmate because that is what the dominate cultural message pushes even if they aren't particularly suited to it and that is unfortunate. The solution though is not to tell people that they have the wrong number of partners but rather to just keep on insisting that there is no right number. Nobody should be saying that you need to have two in a relationship, nor should they be advocating more than two, nor one. There is no number of partners that will make everybody happy and trying to set one, any one, is a disaster.
The simple fact is that different people have vastly different needs and what relationships they end up in depend greatly on who they meet and their current situation. If allowed to settle out without any particular goal in mind people's relationships end up in all kinds of interesting places and there is nothing wrong with that. Our entire society, both those in mainstream relationships and those on the wild side, need to accept that other people's relationships are going to be strange, incomprehensible, and different and as long as you aren't part of that relationship you might as well smile and nod. Trying to interfere is only going to get you ignored, resented, or both.