Thank you, Tolstoy. Here's a good piece on the topic. The author is trained in rhetoric and language rather than in law, but it makes what I think is a fair argument:
http://www.politico.com/magazine/story/2015/06/gay-marriage-decision-polygamy-119469.html
I will maintain that, if anyone opposes polygamy but supports same-sex marriage between two and only two people, then that person is NOT committed to fundamental equality in marriage. Any argument that polygamous marriages are difficult to imagine or administer on a practical level ("can you imagine the cost and burden of extending marriage benefits to groups of more than two people?") or that they are deprecated ("that's not what marriage is" or even "ewwwww") and questions like "what are you? Mormon?" prove this.
Also, arguments that polygamous marriage is *by default* unequal and prejudicial to women are narrow-minded in assuming that polygamy must consist of a single man married to (and presumably lording it over) multiple wives. It completely ignores the potential that (for example) one woman could be married to multiple husbands, or that two women and two men could all be mutually married to each other.
If the right to marry is as fundamental as the SCOTUS has declared that it is, and as many other governments around the world have affirmed, then it is hard to see how consensual polygamy could be denied state recognition without violating the 14th Amendment -- other than with resort to some argument that marriage actually ISN'T quite as fundamental a right as Obergefell v. Hodges says it is or some silly argument like "but see, this opinion talked explicitly about two-person unions, you moron!"
I'm not sure what the constitutional or jurisprudential arrangements are elsewhere, but I stand by my view that you are a hypocrite if you claim that same-sex marriage among consenting adults must, under principles of equal access to marriage, be recognized while at the same time you reject legal recognition of marriage between more than 2 people.