Lowering these physical requirements risks reducing the American military’s lethality. A more serious effect of sex integration has become taboo to mention: the inevitable introduction of eros into combat units. Putting young, hormonally charged men and women into stressful close quarters for extended periods guarantees sexual liaisons, rivalries and breakups, all of which undermine the bonding essential to a unified fighting force.

A Marine commander who served in Afghanistan described to me how the arrival of an all-female team tasked with reaching out to local women affected discipline on his forward operating base. Until that point, rigorous discipline had been the norm. But when four women—three service members and a translator—arrived, the post’s atmosphere changed overnight from a “stern, businesslike place to that of an eighth-grade dance.” The officer walked into a common room one day to find the women clustered in the center. They were surrounded by eager male Marines, one of whom was doing a handstand.

Another Marine officer, who was stationed on a Navy ship after 9/11, told me that a female officer had regular trysts with an enlisted sailor in the engine room. Marine Cpl. Remedios Cruz, one of the first women to join the infantry, was discharged late last year after admitting to a sexual relationship with a male subordinate.