> In reality, the money is coming from a corporation, who presumably has already costed the risk and is willing to accept it.

Then his salary, and the salary of all the employees have been lowered to provide the benefit. That means employees without kids pay for the parents.

> Moreover money is not zero-sum.

A handout is definitely zero-sum. But even if it isn't, the entire benefit of that handout is captured by the receiver, not by the giver. So its an even worse reason for an employer to give parental leave.