This comes from a discussion elsewhere, so there's some recap from my earlier post.
When talking about literature, one has to consider what the purpose of "literature" is and what actually accomplishes that purpose.
I submit that, when it comes to written fiction, the purpose (if one goes beyond "make money for the author"--something which I do not disparage for its own sake, but we'll come back to that shortly) is to create an emotional resonance within the reader. The reader reads, and is touched in ways that generate that emotional response.
Now, some folk are given to sneering at "popular fiction", claiming that it addresses the "least common denominator" and, I've heard it put rather crudely "shit floats."
That, of course, can be trivially dismissed. If it were that simple, then anyone could to it and sleep on big piles of money from the sale of same. Excuses abound for why proponents of that theory don't do it but as we go on and on and so very few do demonstrate that "anyone could do it", it become eminently clear that the reason they don't is simply that they can't. The "theory" doesn't hold water.
You see, for fiction to be popular it has to strike a chord within a broad swath of the population. That's less a prescription than being very nearly a definition. If it doesn't strike that chord then people won't decide that book is worth more than the six pack of cheap beer they could have otherwise purchased and the book doesn't get bought, and certainly doesn't become popular.
So, to be popular, fiction must strike something within people's hearts and minds. It must resonate with many people. It must tap into the heart of what makes us human. Jung might call that the "collective unconsciousness." Whatever you call it, it's something that, without which, fiction cannot be popular.
That something can be base in nature--appeal to sex drive and titillation, for instance--and some areas are certainly easier to get that emotional connection than others. But that very ease only speaks to how very powerful the emotional drive in humanity is. Porn, to use the classic example, is an economic powerhouse precisely because the drive is so powerful. The danger with that one is that it is so powerful that in stories that evoke it everything else gets lost behind the power of the sex impulse. And the stories become only about sex, with the rest being mere window dressing.
But another drive, one nearly as powerful, is that toward what we can call agency. Whether a person has control over their own life, or not. I note that a lot of "literary" fiction is about the lack of agency. They are overwhelmed by events, swept along by circumstances over which they have no control. Popular fiction often takes the other side. People's fates are to a greater extent their own. While they may face enormous challenges, their actions matter, if only to them. Agency is at the core of both events of the story (plot) and character development.
Now, some people might claim that that's unrealistic. That people have little control over their own fates that they are swept along by events beyond their control. Perhaps. In some places and some circumstances. But he idea of agency is deeply rooted even in classical literature. In Shakespeare's tragedies, for instance, the tragic characters build their horror with every choice they make. the events are only tragic because of the choices the characters make. If Hamlet had made choices of the kind Othello would have made, he would have carved Claudius like a suckling pig the very night the ghost told him of his murder. If Othello had made decisions of the kind Hamlet would have made, he would have delayed and waited, and checked and double checked until Desdemona's innocence was at last revealed. In neither case would the story have been a tragedy, not in the classic sense. They built their prisons, brick by brick.
And so, it would appear, agency is at the heart of much, if not most "popular fiction" (genre or not). It also appears to be at the heart of that "classical literature" that people actually read and enjoy. Shakespeare survives not because professors of literature declare his works as "literature" but for the simple reason that through the centuries people watched and read and were swept away in his work. He was among the popular fiction of his day . . . and to the present time, in fact.
And thus, we see that popular fiction is literature, in the true meaning of the term, in that which touches the heart, the mind, and the soul. Without that touch, nobody would read it. Without that touch, nobody would buy it.