This article comes at the same sex marriage controversy from the same perspective as the video below. Rather than begin with why same-sex marriage is wrong or an impossibility, the argument more logically begins with why opposite sex unions and traditional marriage are necessary and beneficial to societies in ways that same-sex unions can't be either necessary or beneficial. A few quotes:
Governments assign legal responsibilities and benefits to marriage, rather than to other relationships, to help mitigate the potentially destructive and tragic consequences of irresponsible procreation.
Since civil marriage wouldn’t originally arise in response to desires or demands of individuals in diverse relationships, the first move must have been made by governments. Why, then, would governments want to create something like civil marriage?
While many relationships don’t cause any consequences that we might see as potentially problematic for society if left unregulated, one sort of relationship clearly does: sexually intimate opposite-sex relationships.
Left unregulated by the government, most consequences of relationships—such as warm, fuzzy feelings, mutual goodwill, and trust—will not become socially destructive; procreation, on the other hand, is an entirely different story.