I've been working on Barb for a while. I looked at her as a sort of every woman. She's incredibly strong she's incredibly generous. She's seemingly insane because she is in the situation of a polygamous relationship but she had definite reasons to do it.
The state's interest in marriage is stability. Generally speaking polygamy does not work for stability. Inherent in the whole polygamous movement is a deep and abiding misogyny and denigration of women. So polygamy is objectionable on lots of grounds.