The vast majority of the time I prefer to read genre fiction, whether crime or SF, rather than reading literary fiction. I'd go further - I think good genre writing is better fiction than most literary fiction. So I have real mixed feelings about seeing the quotes alongside in the Adam Roberts book By Light Alone, which I recently reviewed.
On the one hand I absolutely agree that Roberts is a brilliant writer. And I think it's true that the literary types (I would hardly describe them as mainstream (or even 'mainstram') will pick up on Roberts just as they did, for instance, with Ray Bradbury, and will do all their power to try to persuade themselves and the rest of us that because this is good writing, it's not really science fiction at all. However, I think it is a sad reflection of the nature of the literary establishment that they feel the need to do this. Roberts writes excellent fiction that makes you think - like many SF writers. And he writes science fiction.
After writing this I noticed in my review of Roberts' book The Thing Itself, I wrote 'This is the kind of science fiction that should be winning the Booker Prize. Simple as that.' It was an interesting echo of the comment above - but I ought to stress I'm not saying that Roberts' books should be considered literary fiction, but that prizes like the Booker should take in genre fiction, because it's so often better than the stuff they get excited over.