The harm feared from same-sex marriage has already arrived: Whether same-sex marriage is accepted or not, opposite-sex marriage as a norm and expectation has already collapsed. CNN opinion piece, typical stuff on research showing children with two parents until 18 do better than single parent families.
A more accurate ending to your article would be “Marriage as a norm has already collapsed, outside of the college-educated. Same-sex marriage has had no effect on this whatsoever.”
This is what Frum was getting at, but still, methinks he is purposefully less clear than he could be. I’ll leave you with this picture. How lucky would you be to have double the amount of grandmas?
Addendum: George estimates that cookie supply would double. I think the effect would be slightly higher, due to synergy.