I think Edgar Allan Poe would be interested to learn that some of his greatest stories would today be slotted into the mystery genre.  Or more precisely, detective fiction.  He might concede that his stories made good use of suspense to propel the narrative. But so did those of Charles Dickens. Acceding to the demands of serializations, he knew his readers would buy the next edition of the periodical only if they had to know what happens next.   Did he see this as being trapped by commercial exigencies, or was it simply good storytelling that any respectable author should aspire to?

Jazz began life in the African-American neighborhoods of New Orleans in the late nineteenth, early twentieth century.  In no way would any music connoisseur of the time have considered it a respectable form.  The accomplishments of Duke Ellington, Miles Davis, and Wynton Marsalis tells us where that ended up.  By the same token, the earliest pulp magazines were unabashedly meant to be popular entertainments, with no pretense toward literary achievement, except perhaps by the writers themselves, mostly in secret.  

Of these, the exemplar was Dashiell Hammett. As with Dickens, his stock in trade were periodicals, in particular the pulp magazine Black Mask, where he published dozens of stories, some as serialized novels.  As Raymond Chandler pointed out in “The Simple Art of Murder,” Hammett was heavily influenced by Ernest Hemingway.  Though I also agree with Chandler that Hemingway was fully aware of Hammett’s contributions to twentieth-century literature, from which he took his own inspiration.  Hemingway might have explored the revolutionary concept, at the time, of the American antihero, though the sensibilities of a character like Jake Barnes, manly and cynical for sure, was also drenched in existential confusion of the sort you can only acquire through an exhaustive and eclectic reading list and lots of time in stuffy parlors with people like Gertrude Stein.  

What Hammett wrought was the pure form.  Sam Spade was a man of seemingly moral ambivalence, coldly pessimistic about human nature, yet at the end of the book, clear-eyed about the distinctions between right and wrong, villainy and virtue.

Jake Barnes and Sam Spade endure inside nearly every subsequent American hero spawned by genre and literary fiction alike, but I feel that Spade ultimately had the upper hand.  With this sort of influence on letters as a whole, what makes the distinctions of genre important?

Since genres are inevitable, maybe we should celebrate the mystery thriller world for being positively bursting with subgenres. Private eye, hardboiled, noir, police procedural, amateur sleuth (where the amateur could be anything from a chef to an antiques dealer to a bipolar circus clown with a drinking problem), cozy (with cats/without cats), historic, erotic, espionage, occult, cyberspace, young adult, etc., etc.  With such a proliferation of forms,  do we need to define the overall phylum as being merely different from some other major genres, say Romance? (Oh yeah, I forgot about romantic mysteries.)

Despite the seeming polemics, I’m not advocating for the abolition of genre classifications.  In fact, there are manifold reasons to have guideposts for book buyers trying to navigate all the possibilities.  I’d hate to crack open what I thought was a beach-read thriller only to find an anthology of fourteenth-century epic poetry.  What I resist are all the biases that accompanying people’s devotion to particular types of reading.  

What I say is to read everything.  To delight in how each reinforces the other and builds a larger universe of creativity and craft.  

There is no hierarchy.  Thriller snobs are no better than literary snobs, and vice versa. They both have closed their minds to the dazzling wealth of the written word, and the endlessly involving paths to satisfying storytelling.  To say nothing of the sheer joy of well-crafted prose, in any form.