I think you're exactly right. I recently wrote about the unretouched nude the Lizzo posted on Instagram and got a lot of push back - from women. "She's promoting unhealthy behavior" even though Lizzo wasn't promoting anything other than self-acceptance, AND recent science shows that about half of fat people are metabolically healthy, something that many thin people are not. What they really didn't like was that she was not sufficiently ashamed of her body, as they feel she ought to be because they see her as inferior and don't like that she's not acting as if she is.