"I too-often see (almost always white, almost always male) commentors and bloggers saying that they don't have a problem reading books in which the protagonists are aliens, or elves, or women, or black people--so why is these so much fuss about the need for diversity and representation in literature?"
This is an argument which interests me, because five years(ish) back when *I* was a fledgling LJer I made that very argument; and I think no less a light than you challenged me to actually *count* what I read, and I did, and was appalled that actually I mostly read straight white men writing about straight white men. Less privileged groups are more *noticeable* in our reading *because* rarer; anyone who says they don't have a problem without actually sitting down and thinking about whether it's true is almost certainly wrong.
I know I was. Hopefully, if I said it again today, I wouldn't be.