Indeed, I would suggest that the question of whether polygyny should be allowed is in many ways not so much a moral issue as a practical one. Since multiple men cannot share a woman (if they did, they wouldn't know whose children were whose) then unless there are many more women than men, allowing some men to have multiple wives would produce a shortage of women.
To be sure, women are well within their rights to insist that they be their husband's sole love interest, and I suspect the vast majority of women would so insist. But polygyny is far less morally dubious than the 'same sex marriage' notions that have been being pused lately.
They can insist all they like, but it'll be up to hubby who he marries. Then her household assets have simply been divided and lessened, and her children's family status threatened. In the post-marriage world, if everything is marriage, nothing is marriage.
I know of a very affluent liberal couple--she's High Maintenance to da max. They are most vociferously in favor of same-sex marriage. I think I'll point out that shortly nothing will stop her from being only one of SEVERAL trophy wives...not only will she have to share hubby (no great sacrifice), but hubby's checkbook. Heh.