That's a hollow argument, usually perpetuated by those not in uniform. If it does happen, its a failure of discipline and traning on the part of the men, not the women. Note that nobody ever invokes the "Mother Hen" argument, in which a female soldier takes unnecessary risks to save male counterparts from danger?Without doubt some are. However, of far greater concern (beyond the physical) is the "little sister phenomenon" this isn't much of a factor among pilots, or engine technicians or ships company although it is there. It certainly does, however, become an issue in units in ground combat where men are going to risk their lives when it is a woman in a way that they wouldn’t for another man in the unit.
Further, I am aware of no instances in recent combat situations where male soldiers died unnecessarily saving a female (who has the same training and equipment etc) from danger. Anyone know of anything more than supposition and anecdote?