It isn't designed to stop them from having sex, its to prevent them from getting pregnant while on deployment in a war zone and subsequently losing another soldier.
Seen this many times myself, have even heard a female sailor specifically say that would be her intent to get out of a deployment by timing her pregnancy to correspond with it.
There is nothing woman's rights groups will be able to spin out of this one, PC is not an issue. Commitment by our military is ever demanding and expected, to circumvent that is detrimental to all the others that serve.
Here in Canada, women are allowed to get pregnant while enlisted. I just googled it.
To all the hot American soldier girls: come fight for Canada!
They can in America as well, just not in a war zone or timed to get out of a deployment.