Proponents of the idea of marriage have always held that the institution exists primarily for the rearing of children. If the marriage ideal consists of a husband and wife raising children together, anything less is a degraded version of the ideal.
Unless adultery or abuse is occuring within the marriage, what needs to be considered is how an intact marriage affects the ultimate potentiality of the children reared within the family. If you say "plenty of good people have been raised in non-intact familes," I can ask "but how much better would these people be if their parents had remained together?" And if you say "plenty of stinkers have been raised in intact families," I can ask "but how much worse would these people have been had their parents' marriages ended in divorce?"
I suppose, if your notion of "essentiality" merely encompasses "that which might lead to a positive result," the notion of intact families is neither here nor there. But if the idea of the essentiality of intact marriages encompasses what is best (and not merely adequate, or merely better than some other arrangement) for the child within any traditional standard, intact marriages are essential for children. One need look no further than the inner city of your nearest metropolis for proof.