I've yet to see any study convincingly refute insulin's effect on fat uptake (also: we've known this for like a hundred years).
I don't really disagree with anything else you've said, but here's why this topic tends to get to me: with most other illnesses, we don't automatically assume the worst about the other person and assume it was their behavior that caused it. (while, incidentally, knowing nothing about their behavior). If someone got brain cancer, we wouldn't be like "looks like you used your phone too much!", and if someone is going bald you wouldn't be like "looks like you accidentally replaced your shampoo with Nair!"
Obesity is a symptom of quite a few underlying diseases. You can become obese from overeating, sure, but you can also become obese by getting a brain tumor in the wrong spot, or because you handle specific foods poorly, or you have endocrine issues, or your gut bacteria have become unhealthy, or... (lots of reasons). We act like obesity is the cause to everything, when it's often just a symptom.
When people frame this in moral terms ("you're fat because you're a glutton"), it just strikes me as clueless, because we have this rising obesity epidemic on our hands, and it seems really unlikely that somehow our generation is special in terms of just not being able to resist an extra slice of pizza.
You would think that with all the reproducibility issues around various topics we'd know better than to assume we completely understand human metabolism. If we're wrong, how much damage is being done?
Btw, do you have citations for these?
Is this clear, though? Many people can manage their weight by increasing or decreasing food intake.
It seems more likely that under normal circumstances weight can be easily managed, but other factors can force someone in either direction. Thus Alice doesn't understand why Bob is overweight and Charlie is underweight, because whenever Alice gets chubby or skinny she can easily get back in the normal range. For Alice, staying in shape is so easy that obesity really would be a sign of gluttony and being underweight would be a sign of mental illness, while for Bob and Charlie getting in shape would first require removing environmental factors.
It feels like there are a lot of Alices and a lot of Bobs that both argue with each other as though their own experience applies equally to everyone, which probably isn't true.