They are strictly less efficient than commercial daycare because the adult-child ratio is much higher. How many women would be of out of the work for if they were taking care of children?
Also, it prevents trickle down and the lifting of the poorest in society.
If your position is that people should not be compelled to contribute to overall society and the lifting of the boats of others, than there isn't enough alignment of values for a meaningful conversation.
I suspect there will be some fraud (I have 30 kids, wheee!) as well as foster/adoption abuse -- probably AZ's experiment with paying parents to home school would be instructive.