3. Young adults, who are aware about romance. They require a lie that romance exists, i.e. heroics, meaning of life, God, etc.
And which seem to require vampires or zombies.
No, because they imply its work of fiction.
I agree that if the writer claims it is a work of fiction, and they defend their story as a fiction, then that gets them off the hook. They enter an agreement with the reader that the story is not true. But they also enter the agreement that for the purposes of the story, the reader must believe that it is true within the context of the story, and that nothing in the story should contradict that truth.
If the writer claims that the work is non-fiction, than different rules apply. And those rules can be broken to the detriment of the credibility of the writer. John Steinbeck's Travels With Charley and Truman Capote's In Cold Blood have been shown to have passages that the writer made from whole cloth, for the purposes of keeping the narrative going. These were teased out later by other writers who researched the stories on their own. That doesn't make them less entertaining as stories, but it does introduce an element of doubt as to their veracity.
Laura Hillenbrand's Seabiscuit and S.C. Gwynne's histories of the Civil War are claimed by the author that everything that the characters thought or said in those recounts could be documented. Is that true? Nobody has been able to fault them so far, AFAIK. That leads me to trust those authors.