Okay, I'm posting...just one more time.
Men do not have an inborn instinct to protect women. It's cultural, if anything. And, with the level of brainwashing that occurs in military training, it's something that can easily be dealt with.
Do we really want soldiers trained to not be protective? That sort of training would be almost certain to cause problems both in action, and when they come home. As much as some liberals would like to pretend we can shunt the military off into some never-never land where they never have to come into contact with civilians, that ain't the case. And as much as some conservatives would like to pretend that we can train finely-honed killing machines who can turn off their aggression at the flick of some inner switch, experience has shown that really isn't the case.
That said, I'm not particularly worried about the effects on combat ability if we were to completely gender integrate our military. For one thing, I don't expect a flood of G.I. Janes in infantry foxholes even if we did. For another, our current areas of combat operations have so little to do with the concept of front lines, that we can't say that women don't regularly serve in combat now.