I use to live somewhat close to the big polygamists settlement in southern Utah... And those people were crazy! It probably has more to do with their religion than the practice of polygamy, but there were so many problems with abuse in their society...
Personally,I don't support the practice at all... But I imagine in a limited case by case basis with everybody consenting to it... I wouldn't oppose other people's right to it. I do have issue with societies built around polygamy like in southern Utah and the history of my own church. People should never feel pressured or obligated to enter a situation like that...