I don't think addicted is the right word. Nicotine is addictive. Some people who aren't addicted to it just smoke because they don't care much about the health effects. So I don't get it. All you have to do is keep the donuts away from your mouth. Or at least exercise it off. You can't undo it when you've smoked, but you can exercise to burn the calories. At least take a walk. How many people actually have thyroid issues? 2% of the population?
Further there are studies showing that administration of opioid blocking drugs also drastically decrease consumption of high sugar foods.
Anorectics work on the brain's pleasure center to drastically reduce appetite. So do addictive drugs. So does food. If there is a pattern of chronic over-eating, the brain adapts and begins to require that type of eating in order to experience a "normal" sense of pleasure (hint - tolerance and addiction also work in this manner).
What you are saying is no different than telling a smoker that all you have to do is keep the cigarette away from your mouth. No ****. If it were that easy I'm sure addiction rates would still be at the level they are now...
And you are right, hypothyroidism, chronic administration of corticosteroids to modulate the immune system, and other homeostatic disorders (leptin and ghrelin, Cushing's, etc) that cause obesity are the exception, not the rule. What is incorrect is labeling any overweight person as "weak" simply because they can't stop eating the way they. That just isn't true.
One of the best ways I've heard it phrased is - Sure it is hard to never touch heroin again if you are addicted to it. But what if you are addicted to it but are required to use it multiple times per day just to survive (since you must eat to live) after having been addicted to it. That level of addiction control is much, much harder if not near impossible.