It seems to me that the decision of whether or not to divorce should be entirely based upon what would be best for the children. In cases of abuse or serious addiction divorce will almost certainly be better for the children. Other situations need to be taken on a case by case basis.
Children must be the focus. If, as I believe is the case, most parents are willing to die for their children, they should be willing to stay in an unhappy marriage for their children as well.