I haven't bothered to read the USMC thing but I can say this.
When it comes to combat, it isn't a matter of gender, its a matter of biology & evolution. Here is one, indisputable fact.
* when one compares a male and a female pound for pound, one learns that the female's heart is smaller.
Its related to evolution and goes back to humanity's 'hunter/gatherer' days. And when it comes to physical stress, there are consequences. If one takes a male & female of identical height, weight and strength, and push them both to the edge of the male's endurance limits, bad things will happen to the female. Up to the point of stroke, heart attack and death. A female's heart is simply not capable of moving as much blood as a male's - which results in oxygen deprivation much sooner for a woman than a man.
Ever wonder why men and women complete separately during marathons ? Even though they start running at the same time ? And even though they start running at the same time, the 1st place woman is always behind the 1st place man ?
Smaller. Heart. (Pittian dots for emphasis)
Here are the Boston Marathon results in easy to read graph form. Women were 'unofficial' participants until 1960, so data before then is spotty at best. The chart contains record breaking runs only, but the point remains.
Its also why I believe men who have transitioned to women should not be allowed to compete in women's divisions of sporting events. The transgender will have an unfair advantage.
So yeah, its not sexist - its biology. If you DUmpmonkeys don't like it, blame evolution.