Court decisions invalidating man-woman marriage laws frequently rely on the argument that expanding marriage to include same-sex relationships would have no social downside and, therefore, cannot be constitutionally justified. However, contemporary social theory casts doubt on this “no downside” argument for genderless marriage. Drawing on social philosophy, especially that of Johns R. Searle, this Article argues that redefining marriage to include same-sex couples will alter the institutional function of marriage, which alterations would have harmful effects on social welfare and children’s rights. This Article further asserts that American courts and commentators are amiss when they mask or willfully ignore the plausible forecasts by gendered marriage advocates that redefining the marriage institution would have harmful social effects. Instead, courts and commentators ought to balance the probable social benefits and costs of the competing conceptions of the marriage institution.