I'd like to start my first post on this topic by saying that I believe in equal rights and responsibilities for all individuals regardless of gender, but I do not think this necessary translates into equal treatment in all things. When people discuss equality of the sexes, I believe they're referring to legal/civil/societal equality and not like... true equality, because the various genders are not completely equal in all things.
There are fundamental differences between men and women biologically that give advantages and disadvantages in certain tasks. As has been stated, men tend to have a physique that lends itself well to brute-force physical labor whereas women tend to be more agile, et cetera, but the differences don't stop there. There are differences in the brain and how men and women are hardwired to think and the areas in which they excel academically.
It's hard to impossible to say what effect our society has on the studies that show the gender differences in the brain. Last I recall, the research indicated that we don't really know if these differences are partly in due to different standards, stereotypes, and paradigms applied to the sexes creating a different development environment or if humans have innately different brain chemistry, structure, and functional capacity. It really doesn't matter though. Societal progress is a slow process. In as much as 10 years it's unlikely there will be much erosion of gender differences in the brain even if our cultural environment is the culprit.
The point is, people are different, and part of what makes society productive is people choosing the tasks that they are best fit for. But at the same time, another thing that makes our society productive in general, is the ability to let people follow their dreams. The effects of having gender as a factor for consideration in our military are far reaching, in many ways that I don't think people realize.
For a lot of people, being part of the military is a defining experience. It can reform troubled individuals, teach you important skills, and develop character. After your service you have access to special educational opportunities as well as veteran's care. Plus we look upon veterans with such reverence; it seems wrong to rob women of that potential. Granted we don't deny them the opportunity entirely, but we limit their potential.
I think what it comes down to is you need to balance practical considerations with theoretical principles. We can't let women into the military into positions that they essentially cannot do and pushing them out entirely is simply unfair. Even applying the same standards of recruitment, testing, and physical fitness to women and men wouldn't be a sufficient way to gauge their usefulness, as there are many problems with having integrated platoons, PMSing can be a complication, etc.
What it comes down to for me is, I have faith that the military's policy is based on the expert opinion of people with the right ideas who have studied and considered the situation more carefully than me. I am not an expert; my opinion is simply that of a layperson who is poorly informed compared to the people who made the call. That isn't to say that I don't hope the policy evolves more over time, I do, but I'm confident placing my trust in experts.