when we’re really just talking about the average slightly overweight/obese people

Are we though?

I think the discussions here are mostly coming down to what you think you’re arguing about. Because there certainly are some crazy claims made by the body positivity movement as well. Even if the core message (“your dignity as a human is not bound to your body shape”) is something basically everyone can agree on.

So the big majorities on both sides argue against the other side based on some fringe opinions. And since one rarely explains their position in detail on the Internet neither side is aware that they actually have a lot of common ground.