Polyamory is what you get when you allow for loving more than one person but are still bound by the idea that whatever applies to a man must also apply to a woman.
A common retort of Westerners to mentions of traditional polygyny is, "Well, if a man can have more than one wife then a woman should be able to have more than one husband," and polyamory is that retort enacted in people's lives. (Never mind that women on the whole want no such thing, it's more important to prove a point than to listen to what your insides are screaming, right? Abstractions trump lived experience. Such is the Western mind.)
Polyamory is plurality minus hierarchy. Plurality minus traditional gender roles.
Polyamory is what people come up with when they seek to bust out of monogamism without questioning egalitarianism.
In polyamory, a man's women are not his own; a woman can join with whomever she wishes.
Among polyamorists, drama and jealousy are rife and maturity is ascribed to those who show resignation in the face of chaos.
Fairness is the highest good while the most evil is "patriarchy" — because girls raised under its influence might see themselves as different than men and (gasp!) not aspire to take the place of men. And that wouldn't be "fair" — fairness being the ultimate abstraction. This, you knuckleheads, is why polyamory is okay when polygyny isn't. Think of the chiiiillldrrenn...
Children who, by the way, are owned by that great abstraction, the state. The thing that will take them away without blinking. Polyamory is okay because it's no threat to the state. It has no tribal power. Polyamory is loving more than one but not crossing that line.