I don't know why the only thing anyone's talking about is the polygamy. It's not uncommon in their world and it's not as if it doesn't exist in ours.
There's plenty of polyamorous people, folks with open relationships, close-knit swingers, multi-marrages (even if not legally allowable). It's just not normal, so people gawk and talk and look down on folks for what makes them happy, so you almost never really see it.