It is easy to interpret the popularity of a network television series like “Modern Family” as proof that we have mainstreamed the various and sweeping ways domestic life has reshaped itself over the past two decades. A nation of squares would not embrace a comedy about a badly dressed, middle-aged gay couple raising an adopted Vietnamese baby, we tell ourselves, no matter what they might say in Copenhagen or Berlin. Gay rights are moving forward; single women now account for 41 percent of all births. Americans build caring families with lovers, friends and neighbors; from one-night stands and anonymous providers of genetic material. And yet, even in a place as progressive as New York, the legal system has been slow to synchronize to these altered realities. It is hard to imagine anyone experiencing this more viscerally right now than a man named Jonathan Sporn, a 54-year-old pharmaceuticals executive living on the Upper West Side, who in a sense has fallen prey to a system that excessively privileges the conventional family models from which there seems to be a growing exodus.