Sherif Girgis, one of the co-authors of What is Marriage? Man and Woman: A Defense, opines at Public Discourse about a "bad argument" that needs to be put to rest - namely, the argument that "laws defining marriage as a male-female union should be treated as forms of sex discrimination".
The Supreme Court closely scrutinizes policies involving racial, sexual, and other "suspect" classifications. But unlike almost every other classification imaginable, marriage laws use a criterion necessarily linked to an inherently good social purpose that we didn't just invent. This criterion isn't truly suspect and shouldn't get heightened scrutiny.
The primary question regarding the definition of marriage is not whether any particular class of individuals (gay, straight, male, female) has a special link to the common good, but whether certain couples do. And it shifts the burden of proof onto those who would find no such link.
Read Girgis's whole outstanding essay today.