I'm going to tell my girlfriend that fatherhood and motherhood are fundamentally different
C'mon! What is the difference between fatherhood and motherhood?
Mothers and dads have different responsiblities when it comes to having a family.
That is not true. They both have the same responsibility of raising the child. There is no difference.
There is. She coddles the child, and I am supposed to be rough with the child.
It is not necessary to do that or to think like that. You both play equal parts in raising a child, and there does not have to be a philosophical difference.