Thank you for this!!!! I wrote about this topic months ago and while I got some love, boy did I get the hate! I'm thin. I've always been thin. I'll likely always be thin. As a teenager, my ribs stuck our further than my damn boobs. People have constantly felt it okay to say shit to me. People seem to think it's funny to post memes saying stupid crap like "real women don't wear a size 0." Well, I do and I can assure you, I'm real.
It feels like in some respects and to some people, not all, but some, body positivity is nothing more than turing the hate big girls have gotten for ages back onto thin girls. That's not positivity. Negativity doesn't breed positivity.
Like you said, just leave people's bodies alone.