How do you know that "healthy people would feel shame if they got obese" -> "healthy people use shame as a motivator to maintain weight"? Doesn't that rely on the assumption that shame works?... but that's precisely the thing I'm questioning. I don't actually know shame works because I don't see evidence that healthy weighted people have more shame, are more sensitive to shame, or are shamed more often than fat people. If anything fat people have the most shame, are the most sensitive to being shamed, and are publicly shamed more often... and they're still fat.
30 years ago you would have gotten shamed if you gained a few pounds, that early signal makes people think about eating habits earlier and makes many people never go into unhealthy weight in the first place.
So even though shame might not work to get fat people to lose weight, it could still work to keep people from ever getting fat. Getting shamed for a few pounds means that you can fix the source of shame by dieting for a few weeks, very doable for average people.
Where is the evidence that shame has a causational relationship with people getting fat? You're still only pointing to correlation and saying that because shaming was more common in the past, shaming is effective now. This implies that healthy weight people respond to shame more strongly than fat people or something, but that's just not true in my experience.
