Also the vast majority of civilisations that we know about have been multiple partner arrangements. Usually due to resource constraints I would guess. http://en.wikipedia.org/wiki/Polygamy#Patterns_of_occurrence_worldwide
“According to the Ethnographic Atlas Codebook, of the 1231 societies noted, 186 were monogamous. 453 had occasional polygyny, 588 had more frequent polygyny, and 4 had polyandry.”

It is immoral, unless you think that children are harmed in this type of arrangement, to not allow these people the same rights as other consenting adults.

I feel like a dunce now. I deserve a poly-abusive marriage.

Such power insight indeed.