Er, I see a few problems with that argument. First, what marriage is "viewed" as is very different from the reality of it. The reality is, people marry for a whole assortment of reasons, many outside the traditional "view" of marriage. I've known people who've married for the following reasons. Guilt is one (usually for knocking someone up), just for the children's sake, another to secure permanent residency status for another, status (yes, it happens with monogamous marriage), to be a freeloader off the more wealthy spouse, and actual love. Some will use marriage (as they already do) for commodity's sake, so what? Why is it ok for a monogamous marriage? Who's to say the rich don't already kind of do this, since after all, they almost always have multiple mistresses. If anything, letting them marry their other mistresses will possibly improve those relationships, since after all with a marriage, they couldn't just dump them and expect to get away scot free (alimony, which may actually discourage frivolous multiple marriages) But aside from the commodity aspect, which already happens, I don't find that a particularly good argument to deny polyamorous couples from the right of marriage, or otherwise legal recognition.