Fight it or… not commit to such a person at all. It’s too important for me so I talk it through much earlier into the relationship.
That’s the issue right there, isn’t it? If both partners are believers at the start of the relationship, then one becomes a disbeliever, does that impact the decision-making process regarding the children? Their marriage vows centered on a mutual belief in God… this issue wasn’t something that they could have discussed or prepared for before they got married.