I think with the way we are now fighting combat, its inherent that women in the military be given some sort of basic infantry schooling. The Marine Corps already does this with ALL of its non infantry MOS, male and female. All Marines, regardless of their respective job, are basic riflemen. Meaning we are all trained in basic squad mauevers, special weapons firing, MOUT, etc.....I think its important(and the Army has toyed with the idea as well) that everybody be trained in some basic infantry tactics, since the attacks come from anywhere and everywhere. Its folly to have females serve on the ground as supply personell, and as in the case of Jessica Lynch, hand off their weapon to someone else when attacked. A female Marine would have likely fixed her bayonet if it came down to it.
However, even though all female Marines go through this extra training, they are still segregated from the males, just as they are in boot camp. And as was mentioned before, females do have different standards for physical strength testing(and I believe they get a few extra minutes to complete the run). Once they reach MOS schools and fleet units, they are integrated with males, and are expected to be able to perform their job, and develop the same leadership skills in the same manner a male is. So if they are going to be in a support role, they should be trained in some basic infantry tactics, since there is a chance they could be faced with an ambush.
But should they be pure infantry in their roles? I don't think so. Its not a knock on their capabilities, but rather that as a society, men are expendable. I've used this example before, using really simple numbers to illustrate the point. A country has 10 men and 10 females. They come under attack. half of the 20 people will serve in defense. Of the 10 that fight, only two come back. In scenario one, 5 males and 5 females were sent to fight. 1 male and 1 female return, giving the society a total of 6 males, and 6 females. The highest possible birthrate over the next year(to replenish the society) is 6 children. In scenario 2, all 10 males are sent to fight, whilst the 10 women stay behind. 2 males return. The highest possible birthrate over the next year, is 10 children. So we can effectively shrink the male population down to a small number, and still experience a greater population growth, than we could if we sent an equal number of women into obvious combat situations. If you put it into the context of women having 2-3 kids over the course of a lifetime, you can see the numbers would even more greatly favor the scenario where men are sent into the heart of the matter.
Its really the only rationale I can think of, as to why we have ever kept women out of combat. A natural inclination, as a species, to keep the baby farms alive and protected, so that our species can expand and grow. Its evident in some aspects of nature(think lion prides, one or two males, several females).