sympoze

So some of you may be worried that the Salt Lake City air is getting to me.  But this is something that I've thought about for a while now and only finally getting around to putting into pixels.  One of the presenters at the NEH basically made the same point in passing today, which reminded me that I'd never posted on it.
Here's my claim: the arguments for the legitimacy (whether we're thinking legal or moral here, I don't think that it matters) same-sex marriage can also be used to establish the legitimacy of polygamy.  Now, I'm not making a claim about either the strength of the arguments here or the truth of their conclusions; I'm making only a claim about the relationship between two kinds of arguments.
Take any plausible argument for same-sex marriage; for instance, consider the general argumentative strategy that marriage is a civil or legal relationship or contract that consenting adults enter into.  Then simply take that argument and change it from being about qualities of those entering into the relationship to being about the quantity of those entering into the relationship.  If the 'parts' don't matter for such a relationship or contract, I cannot see why the number of consenting adults would matter.  If there is no relevant different between same-sex marriage and polygamy on the basis of social contract or agreement, then arguments for the former can also be used as arguments for the latter.  Sure, there are ways that one could block the move from same-sex marriage to polygamy, but I can't think of any reason why these wouldn't be rather ad hoc and superficial.