Humanity is pretty dim already. This kind of situation is quite complex, from socio-economic factors, education, access to healthy food (including taking the time to cook), to medical issues that are often mentioned but usually dismissed (as I've described in another comment, you can quite easily get uncontrollably obese with an antipsychotic or antidepressive medication -- and given the society's speed of development and ever increasing work requirements, it's not hard to see why a lot of people would have mental health issues) (not to mention actual hormonal disorders that can actually prevent a person from being able to feel full).

In my opinion, it's helpful to look at the human body as a biological machine. The mind itself is at the mercy of it's vessel, the brain. Thoughts are electrical impulses enhanced with chemical neurotransmitters. A change can quite literally cause a person to change their mind (literally, i.e. a hard-vegan and animal rights activist having a stroke and becoming a caricature of a meat eater, in worse cases a complete replacement of someone's personality and memories).

The human body is not below the mind, rather, they work together. An incident can initiate a never-ending cycle that ends in obesity and ultimately death.

Self control is not the panacea people think it is. The concious mind cannot override most if not all built-in impulses. Can you choose not to have sex? No. If you ask "why would I", that is already heavily influenced by the impulses built into the structure of the nervous system. A basic part of human existence. If you get over that part, sooner or later you will experience mental health issues beyond your control and ultimately forget your initial idea of celibacy. I have used this example and not eating, or excretion of waste, as technically sexual activity has no influence on the body's homeostasis and internal proceses.

Some people have a different priority list, including overeating. I do not think that ANY obese person has ever conciously made the decision to overeat and be miserable, sick and die earlier.

In any case, I agree with your part about parenting. It is incredibly negligent. Not introducing a child to the concept of overeating will in a lot of cases prevent obesity. However, some people are biologically predisposed to have less self control. This does not have to imply obesity and overeating.

On my own example, I have never smoked a cigarette, taken any psychoactive substance, or drank alcohol. I know that had I done any of those things, it would become an obsession to me. My father is an alcoholic drug addict who smokes a lot. My mother is just a heavy smoker. Some people cannot control themselves, and the long-term success rates of drug rehabilitation and AA/smoking quitters show that.