If by polygamy we are talking state recognition of such relationships, I'm not so sure. I'm not deadset against it, having honestly not given the issue a lot of thought, but my gut leans a bit toward no. I am prepared to be swayed, though. So, if anyone has given it some thought, and wishes to post pro or con, I'd be interested.
I've known a few "family groups" in the Pagan community who were unofficially polygamous and polyandrous. I've never seen one that worked for any length of time, not to say that it couldn't. There never seems to be an equal division of love.
One problem, as things stand now, is that since polyspousaly (or whatever you want to call the general term) is not officially recognized, it is quite possible that one or more members of the union will be cheated if they break up. Now I can see why this would be a nightmare for the courts to try to resolve, so about the only way I would support it becoming legal is if it
required a prenuptial agreement by all members of the union.
That being said, I have known more than one couple of what you would assume to be average married couples, in which one or both members have a lover on the side of which the spouse is not only aware of, but approves of. They are not a unit, but there is an agreement. These usually don't work for long either, but they have a better chance than polyspousaly.
***
But of course, I am reminded of a joke. It is at a cocktail party where wealthy couples are gathered
Wife: Phillip, I saw you kissing a pretty girl I've never seen before, over by the hors d'oeuvres.
Husband: I should confess to you my dear, that is my mistress.
Wife: Oh Phillip! I cannot abide that. I want a divorce.
Husband: Well, if you must, my dear, but you well know that our prenuptial agreement would mean no more world cruises, no more mink coats and no more Rolls Royces for you.
Wife: I... I will have to think about it.
Husband: You do that my love. But really, it is not so odd. You see that girl over there kissing Edward? That is
his mistress.
Wife: Ours is prettier.