As this is an open letter, I believe it deserves an open response:
You're pretty much right categorically and without exception, and I'm sorry to have mislead you for a moment into believing I think anything different. I will say that the book of mine you threw across the room is, in part, actually intended to address the point you make about it, but I obviously failed for you as a reader in doing so, and I'm sorry.
That racism serves a story is never an excuse, especially if the racism is unexamined. There's a fine line to walk, of course, because it's also racist to make people of color sacrosanct in fiction. The only long-term solution I am aware of is saturation: getting enough characters of color out there that each one stops being special by virtue of their color.
When I said that sometimes it helps to write as if somebody "happens to have" a particular background, what I meant was not that anything else is the default. I meant that the character needs to be a person first, rather than being a stereotype or a token. A person, in other words, not an archetype or a stereotype or a role.
It's a hard thing to talk about, to explain, and we've seen enough evidence already this week that the same words can sound very different to different people.
My intention really is not to earn brownie points. It is, hopefully, to do something about your pain and lack, and my own pain and lack, and the pain and lack of my friends and family and random strangers on the street.
If I check in with friends to see if I'm making mistakes, it's because I would rather be part of the solution than part of the problem, and obviously I'm not doing it well enough yet.
ETA: Think VERY CAREFULLY before you comment on this post. And make damned sure you are being both polite and respectful of others when you do. Or I will close comments.
Oz has spoken.
deepad's essay, here, is also excellent.
(I do wish people would stop assuming I'm straight.)