Hypo re the pedagogical function of marriage law

A blogger at Megan McArdle's site poses the following hypothetical to pro-marriage opponents of same-sex marriage:

An 8-year-old goes to play at the house of his friend, who is raised by two lesbian women. The environment is a loving one. So this playmate, whose straight parents are married, is going to absorb one of two possible norms.

1) My friend lives in a happy home. His parents are married. When people grow up and love each other, and want to have kids and a happy home, they get married. (I hope I get married one day.); or

2) My friend lives in a happy home. His parents aren't married. When people grow up and love each other, and want to have kids and a happy home, sometimes they get married like my parents. Other times they don't get married, like my friend's parents. (One day I may get married and have kids, but maybe I'll just have kids and live with the person I love.)

Shouldn't we prefer option #1 to #2?  Some might try an option #3, arguing that good parents shouldn't be allowing their children to play at the home of children with two lesbian parents in the first place.  That suggestion makes no moral or practical sense to me.  Other options -- some more thoughtful than others -- are discussed in the comments to Eugene Volokh's post of the hypo.