As to "radical social engineers on the left", I can't agree with you. I've never heard anyone, not the staunchest liberal or feminist, argue for numerical parity in the military or in combat. The number of women who would want to go into combat and who qualify is very small. Even if more qualified I doubt large numbers would want a combat deployment. And I don't know of anyone who is pushing women into combat roles. Most liberals and feminists are anti-military and anti-war across the board. They really aren't clamouring for women to be in the military let alone combat.
Meanwhile military service is voluntary and likely to stay that way. There is no quota system for females that I'm aware of in place to fill military positions. There are overall recruitment goals which haven't been met in 11 years. The number of people applying falls short and the number actually fulfilling their enlistment agreements falls short of military goals.
Therefore, there is no reason for the military to accept unqualified or less qualified people unless they simply don't have enough applicants to fill positions. This is a separate problem the military seems to face. If we want more men it would seem to me it would be smarter to heavily recruit and incentivize men, rather than whine and complain about "lower standards" for women.