I think the problem with polygamy (and there is rarely polyandry) is that it's generally built on an assumed inequality between the sexes. From a legal perspective, it kind of requires this assymetry - the wives are all seen as pertaining to the husband in some sort of "hub and spoke" arrangement... in many cases it's pretty close to direct ownership. It's hard to square this with the idea of a marriage of equals.
It would be very hard to legislate for in a western context based purely on these gender equality grounds, but also, given the cultures in which it occurs (mostly fringe religions and weird communes), there's too many issues of power imbalance for it to be a simple question of consent.
It would be very hard to legislate for in a western context based purely on these gender equality grounds, but also, given the cultures in which it occurs (mostly fringe religions and weird communes), there's too many issues of power imbalance for it to be a simple question of consent.