Harmful for the same reason as the 'healthy at any size' campaign, and anti progressive because if they claim health at every size, then they deny there's a huge malnutrition problem in America. It would be solving the problem of food deserts and obesity by just saying 'no no these people are actually healthy' instead of making sure they don't live in a fucking food desert.
Well for starters, it isn't "healthy at any size", its "health at any size" which is more about making sure you eat and exercise correctly even if you're fat. While I have mixed feelings about the instagram post, OPs argumentation is kinda stupid lmao. Reminds me of r/fatpeoplehate on reddit.