The premise here is that opportunity wasn't equal to begin with. To accept this premise, you have to also accept the premise that societal restrictions on the roles permitted to women, culturally imposed limits on womens' ability to gain power and authority (the "glass ceiling") and persistent beliefs about women being intellectually inferior to men in regards to certain fields, would lead to a status quo not of meritocracy or equality but prejudice against women in an otherwise 'unbiased' system.

And so, to further the goal of equal opportunity, one must balance an already unbalanced set of scales. Not to do so is merely to accept its bias as the status quo.