I wrote an essay on this a few years ago (it's been a hot topic for quite a while and many essayists have written about it). Conservatives have often said that having women in combat is distracting to the men, but that is just as insulting to men as it is to women. Also, there are enough women popping out babies and we're overpopulated anyway, so the argument that we need to keep women home as baby-making machines doesn't hold water anymore.
The truth is, although the rule was in place barring women in the front lines of combat, they were already there and often found themselves in combat. I have a woman friend who served in Iraq, and there is a woman in my neighborhood with two artificial legs as a result of her service in combat. This just makes it official and now no one has to hide it.