When folks have had a child together it's a hundred times worse, cos the bitterness and hatred has another victim to destroy, someone innocent to manipulate in the ongoing vendetta of one-upmanship, another innocent little person who knows mom and dad hate each other, and carry scars for life, with noone to teach them how to live or love.
So you're right. Forgiveness is way better than that. For everyone. But most of all, for the children.
People's anger is so high and their emotional control so low that there is little chance to consider themeselves, let alone the children that may be surrounding them. It is a cycle of abuse much like having alcoholic parents.