I think there is a lot more "personality" at play here than "gender" necessarily. But "gender" is more immediately discernable, and therefore becomes a proxy for having a multitude of personality traits ascribed to someone until they are later confirmed/denied.

An example would be the B.C. described above. Definitely a personality issue, and likely would not cut it in the combat arms.

But I've have a variety of women serve with tank battalions - as medics, S1 personnel, 77F's, etc - and mesh with the team just fine. It was their personality that allowed them to blend in. Someone above mentioned the wife dropping an f-bomb in front of the Marines, and suddenly everyone calmed down. That's a personality that can blend in with the Marines.

Unfortunately, there's no good, objective way to quantify the 'personality' issue such that it could be used as an acceptable discriminator for integrating women more closely into the combat arms, or for placing certain men into mixed-gender situations. Without that objective measure, we're back to arguing about XX vs XY and spinning our wheels.