Just because some people always get upset doesn't mean it's ok to cause upset thoughtlessly.
"bending the knee to political correctness" is rhetoric that shouldn't be seen outside of daily mail editorials. All your talk of arbitrary quotas and paragons of good is just, I dunno, getting excitable over strawmen.
Also whatever elves and dwarves get up to doesn't negate the implications of the way humans are written.
re: the films, Sauron's human allies are reduced in presence, and we rarely see their faces. I recall in teh dvd commentaries talk of finding quite obscure inspirations for their wargear so as to not look too obviously like a parallel for some eastern culture. And Faramir in the extended edition gets a speech where he looks at a dead soldier and says something along the lines of "was this just some regular dude doing his duty like we have to".
So it's not about inserting token characters so much as playing down the Villainous Darkies side.