Campbell seems to argue that the structural components of myth are the product of a universally shared human subconscious. This gives them the nature of self-existent, automatically compelling story elements. I think Campbell has distracted himself with a lot of postmodern psychological mumbo-jumbo into missing an easily hit mark.
The elements of the Monomyth are not self-sufficiently universal.They arise as common situations across cultures due to the universality of human nature - self-interest or self-destruction.
It seems to me that it is always easy to tell a bad application of the Monomyth from a good one: Lazy craftsmen use the structure as a template, mad-libbing scripts or novels out of it. These works have a quality of arbitrary incoherence. The work of skilled craftsmen may indeed contain elements of the Monomyth (in fact, in some cases the Monomyth is so broadly defined that it is impossible to escape), but these elements always arise smoothly and naturally as consequences of the actions and interactions of the players.