Polygamy is normaly accociated with muslims, mormons, and african tribal law, and have gotten a bad reputation from it.
The equality bit is less of a problem in a "hippi commune" but the law will apply equaly to all.
We got a law in denmark specificaly aimed at muslim immigrants, you have to be 24 years old to marry a forenger. That is to prevent the import and forced marrige of somebodys cousin from the home village.
It is a mayor annoyance to other couples where family preassure is not a issue.
I am not sure what other problems it could cause, but it has been out of use in europe for millenia, there must be a reason.
I wonder what it is.