This is a topic over which friends are lost. Apparently. So I'll start by explaining what genre fiction means to me (and not too long ago meant to almost everyone).
Genre fiction is characterized by repetitive structure and tropes. This means readers know what to expect and expect it. It's entertaining. Genre fiction would include romance, mystery, science fiction, fantasy, and so forth. When authors do not adhere to genre conventions--like try to sell a love story without a happy ending as genre romance--readers get upset. Genre fiction is truly a reader/writer relationship based on readers trusting writers to meet their expectations.
Literary fiction (and what I refer to as mainstream or popular fiction, such as Nicholas Sparks) are where writers who don't want to be constrained by genre conventions go to write.
So when my (now former) friend posted that writers should "break all the conventions of genre fiction" the above is the understanding of genre fiction I was working with when I pointed out that breaking genre means you can't sell it as genre. This was immediately perceived as a personal attack and culminated with, "Literary fiction is genre fiction and anyone who disagrees can fuck right off!" (anyone meaning me, if you missed that)
Now, I thought genre fiction was the fiction that literary fiction stared down its patrician nose at. That by "breaking all the conventions of genre fiction" one was, by definition, writing mainstream/popular or literary fiction, which do not have any of the constraints of genre fiction.
If literary fiction is a genre, then what are the conventions that must be met in order to meet the definition of "literary fiction?" I'm sorely tempted to say it's sesquipedalian verbiage constructed into sometimes lyrical obfuscations of extended metaphor indiscernible to the unwashed masses. But it isn't. Or it isn't solely that. So without conventions, what exactly do writers need to break out of...? If you break out of the undefined conventions of lit fic, what are you writing?
Afterthought: fan fiction is another area where writers are "breaking all the conventions of genre fiction" but if you even breathe the term "fan fiction" in the presence of many aspiring lit fic writers fireworks ensue!
Also, while genre fic relies on conventions, that doesn't preclude it from also being lit fic. It only stops being genre when it breaks the conventions of genre. But I remain unconvinced that lit fic as a category is a genre of its own.