Regardless of the legal merit, that is a divisive assertion. The attorneys are trying to put biological parents ahead of gay parents, but in so doing they also make a judgment about all single parents, adoptive families and melded families.
There is no gold standard for parents, and every child who didn't grow up with both biological parents is not lead or tin.
The gold-standard argument is an extension of the "marriage is for procreation" argument, which is itself undermined by all the beautiful childless marriages existing all around us. Not just a politically tenuous position (the number of so-called "non-traditional" families is growing), their argument also promotes the idea that their gold standard families are somehow weakened in a world that allows for alternatives.
The state's attorneys face a steep battle. The U.S. Supreme Court struck down a DOMA that looked very much like Amendment 3. Their hope rests on the courts' willingness to let each state define marriage as it sees fit, an idea that makes these United States a little less united.
Resistance to change is natural, especially change that comes via court decisions in Washington. But this isn't just about a court decision. It's about an evolving attitude across the land, including Utah. Amendment 3 passed nine years ago with 66 percent of the vote. If the vote were held today in what the state's attorneys say is the most marriage-centric and "child-centric" state in the union its passage would not be a sure thing.
Just this week, Intermountain Healthcare Utah's largest health care provider by far announced it was extending full benefits to same-sex partners of its employees. Those benefits will also extend to their children, even though their parents don't meet the state's gold standard.