[webjprgm]

The stay at home parent is childcare. You get personalized child care or you can outsource it for economies of scale and have the second parent work so long as that parent earns more than the cost of childcare.

But I think there's more than just taking care of children. There is research into how important family units are, and those units are better strengthened by greater time commitments of the parents than by less.

Plus there's the issue of parental choice in teaching values. If everyone in the society agreed upon values than the preschool teacher's example would be equivalent. But parents often have their own way of seeing things. Different religions. Different economic and civic philosophies, etc. So there's another reason to increase parental involvement, so that the parents spend more time being role models and conveying values. This is especially true if the childcare is provided as a universal service from the government, because then you can't even choose childcare at your local church.