Not so long ago, adults who read books aimed at a teen audience were either in a minority or hiding their reading material behind a fake cover just in case they were laughed at or considered...weird - this piece by Joel Stein in the NY Times shows what a number of people once thought (or a minority still believe?)
Along came JK Rowling and her young wizard. Reading about the adventures of Harry Potter and his pals was SO inclusive that the publisher produced editions with updated covers especially for the adult market. And it wasn't just the Potter books that received this treatment - Philip Pullman, Mark Haddon, Lian Hearn (to name a few) have also been successful in the 'crossover' market. Twilight, The Hunger Games , The Mortal Instruments Series and a huge number of others have all earned a popularity beyond their intended audience.
The same is true for readers of erotic fiction and the kind of speculative fiction which challenges society's ever-expanding list of taboos. The HUGE popularity of the 'Fifty Shades' trilogy (and its vast number of looky-likey clones) pushed readers from behind their newspapers and out of the dark recesses of their guilt-caves and into the spotlight - suddenly you were weird if you HADN'T read it (I haven't, in case you were wondering, but then I've always been a little weird).
So, I'm wondering - what's next to be crossed off the list of 'Reading Taboos'? Women reading Haynes car manuals? No, wait...that's already been done. Men reading 'Instructions'? Pah, what am I saying? That'll never happen!