Let’s face it: however committed we may be to intellectual diversity and free exchange of ideas, few would criticize a school’s refusal to fund an event in defense of anti-miscegenation laws, or welcome the presence of a white supremacist on a panel about bridging differences. Should the belief that marriage is a male-female union be treated the same way? For many, the answer is yes. At Slate.com, some commenters have criticized the magazine for merely allowing columnist William Saletan—a supporter of equal marriage rights for gays—to argue that opposition to same-sex marriage is not equivalent to racism.

Yet in many situations, we do recognize that gender is not the same as race, legally or morally. In law, racial distinctions are (properly) presumed to be insidious and virtually always illegitimate; sexual distinctions are acceptable with a much less stringent “rational interest” test. The “separate but equal” principle, repugnant as a basis for racial segregation—an analogy commonly used against the idea of civil unions—is far more acceptable for the sexes. Much to the chagrin of radical feminists, there is no taboo on either research or popular discourse on psychological and cognitive sex differences. The backlash against then-Harvard President Lawrence Summers, and his eventual ouster, after he speculated that female underrepresentation in science could be at least partly due to biology was widely regarded as dogmatic intolerance.

In 2000, Andrew Sullivan wrote a New York Times Magazine article arguing that hormones make men and women fundamentally different: men are competitive, risk-taking, action-oriented and power-seeking, women are nurturing, empathetic, relationship-oriented and safety-minded. Personally, I find such claims vastly exaggerated and overgeneralized (Sullivan’s assertions were questioned by many critics, myself included). But are they bigoted and unacceptable in decent society? No. And surely it makes sense that, for some non-bigoted people, the belief in fundamental sexual difference justifies a special status for male-female marriage—not only as a reproductive relationship but as a joining of humanity’s two distinct halves, based on complementary masculine and feminine qualities.