Any social conservatives on HN -- that is to say, both of you -- should keep in mind that if you're worried about how this affects the sanctity of marriage, that institution has long since been sullied by a) allowing government to get involved with it, b) easily-obtainable divorces and c) that whole Henry VIII business. Same-sex couples can't possibly do any more damage than that.
Of the threats to American culture or even Western Civilization as a whole, the SSM boogeyman pales in comparison to a feckless electorate, unaccountable government with Big Brother aspirations, crushing debt and even Islamic extremists.
That's why my reaction is "meh": as a "problem", SSM isn't even on the radar.