I have to wonder, which is more efficient/beneficial for the society, two people both working 7.5 hour days, or one person working 10-12 hours and another staying at home.
I think it depends. In the long run the trap that must be avoided is when women (usually women) leave the workforce after having children since "one parent stays at home" often means "mothers stay at home", after which they have a hard time reentering it (or have to re-qualify/take other jobs etc, which is a huge waste).
If the burden of looking after children is split more evenly between mother and father (say 1 year at a time as long as necessary) and both parents keep their careers afterwards, the difference is smaller. The question is what the state can do to encourage this kind of equality and prevent women from leaving the workforce. The view in progressive economies tends to be that it's long parental leaves, where there is a large part earmarked for the father.
Edit: I should add that the US actually has a pretty decent labour force participation for women. The view that women in the US often end up "homemakers" after having children seems to be pretty exaggerated.
There are countries (Italy and Turkey stand out) where the situation is much worse, to the point where it probably makes a significant dent in the GDP/Capita.
This implies only one of the parents goes to work?