It’s an interesting debate about SF being written by mainstream writers, and whether it is still SF. Most of the early examples are female writers who coupled SF and feminism. Atwood, LeGuin, Lessing, Octavia Butler (who also brought in race topics, of course). Whether you see them as SF or mainstream really depends which editions of their books you pick up. And it really doesn’t matter either way, they were (and are) just good. When it becomes embarrassing is when mainstream writers start playing with SF tropes but don’t have the skill to carry it off well. At the moment I’m reminded of that point in the eighties when mainstream white pop acts started rapping – embarrassing to say the least. You can tell when an artist has a real grasp on the tradition they are working in. You don’t expect classical musicians to be able to play rhythm and blues without at least listening to John Lee Hooker for a while, yet mainstream writers go stumbling into the depths of Hard SF territory without apparently reading any of what has come before. Fair enough if they can do it, but if Cormac McCarthy and Winterson are any guide it seems that they can’t. What’s “rebellious” about conforming to current expectations and ideology? Stereotypes and political correctness are two sides of the same coin, treating characters as statements or representatives and not as individuals.
Quite apart from believing there is space for pure entertainment, I also do not believe that interesting, challenging work usually comes about as a result of a writer sitting down and consciously thinking “OK, I’m going to tackle this important topic”. Writing is more often a process of exploration and discovery, with a lot of unconscious input. As a provision, I would also suggest that the expectation that writers must “treat characters as statements or representatives and not as individuals”, reliable narrators or not, is also a presumption and taste of our own particular time, place, and culture.
Why “must” this be so?
If you’re into SF-done-right, read on.