Horse hockey. How did we manage to fill military manpower requirements for all those years when women were practically non-existent (in the military), and not to be seen in deployed units and naval vessels? Put out a call for more volunteers, or re-instate the draft. But to use the argument that we can't fill our slots with anyone other than women is weak...very weak. Yes, we'd have to change our PC mindset that's been cultivated over the last 30 years, but it could be done.
Scouts Out! Cavalry Ho!
You're actually making my point. The U.S. did not have a problem filling the ranks with men when the military was larger, and even the mere suggestion that a draft might be needed to fill the ranks illustrates just how serious the problem is.
There are a number of factors at work here, including demographics, economic considerations, etc. that make it harder to recruit soldiers today than it was even 20 years ago.