I think women working and both partners needing to work simultaneously are inextricably linked though. While this could be a gross oversimplification, adding 1/2 of the population to the workforce would, through the laws of supplyand demand, decrease wages by 1/2 (assuming that all women were not already dedicated to raising children).
Yes, men can also leave the workforce just as women can enter it, but would a man be more inclined to leave if he was the only breadwinner because the woman was already raising his children? Sorry I know a lot of this may be considered inflammatory but I don't think these questions are being asked (precisely because they may be seen as inflammatory, though my intention really is not to be controversial).