The Utah brief said that redefining marriage to make marriage gender-neutral would break the link between the idea of marriage and the idea of procreation. Utah believes we have a "compelling interest" in keeping children connected with their own father and mother, and if marriage is redefined to wipe out the idea of a united father and mother, children are more likely to be separated from their natural parents. Utah pointed out that replacing a child-focused view of marriage with an adult-driven view would undermine the ideal of father and mother married to each other, raising the children whom their union produces. Redefining marriage will dis-incentivize couples from making sacrifices to stay married for the benefit of their children.
The Utah brief doesn't want to redefine marriage because that will send a clear message that mother-father parenting really doesn't matter. This will mean that fewer children will be born inside stable, loving relationships. That will hurt those children and it will hurt society, too. If marriage is redefined, children will be less likely to be connected to and loved by their own mother and father. We should remember that marriage does not involve only adults; it involves children, too.
Listen to the radio commentary here: