50 percent of combat divisions would have to be women. It would never happen - but there would be significant damage to the combat effectiveness to enforce a dubious doctrine with no basis in reality.
Also - it would mean the end of the US military as a serious fighting force. Men prefer difficult jobs that have a high casulty ratio - why not give men a chance to shine? As a guy I'd be embarrassed to have a woman stick up for me and fight my battles for me even if she had 5 inches and 50 pounds (not difficult), simply because I believe that it's my job to protect her with all I've got.
Why do we have to waste time, energy and money defying what most men and women actually want?