Actually lots of Polynesian societies include a "third gender" of effeminate males who marry other men. I wonder why you never hear the "bbbbut EVERY SOCIETY has always said marriage is man-woman!!!" crowd address that fact?
That really is a stretch.
What? Are you seriously arguing that the fa'afafine somehow aren't a direct, indisputable counterexample to typical right-wing argument of "marriage was defined by every society and every religious group as the union of a man and a woman" 
Colleges and universities do not accept Wikipedia as a source for scholarly writing because of its inaccuracies.
Let's say I give you this one example, out of all the societies and civilizations that existed. If the shoe were on the other foot; if such a group of people were the ONLY group you knew of in the annals of civilization that practiced only man-woman monogamous marriage, would you consider that enough to ban SSM? This example is so idiosyncratic . . . I mean, I'm at a loss for words if one actually believes that this one counterexample offsets the assertion that marriage being between a man and a woman is how every society has defined marriage. OK, every society but one, until 15 years ago. I suspect that this counterexample was known to the plaintiffs who did not point it out because it would appear to support the opposite point of view.
Do you not know what the word "every" means? You said every society believes in man-woman only marriage. A single counterexample is enough to disprove, and I gave you several, since this is common across traditional Poynesian societies. (Not sure where your 15 year stat comes from. Guessing you meant 1500?)
You alleged 100% by saying every. Don't say "every" if you don't want to be disproven so easily.
