It's incomprehensible that it still works this way in a modern economy. The eventual financial benefit of the child goes to society, not the parents, therefore it follows that society should bear the initial financial cost.

There is no eventual financial benefit to having children for society. Our lives would be much better if the population of the Earth was smaller. The oil would last longer, food would be cheaper as we could farm only the most fertile easily-cultivated land, less competition for housing, etc, etc.