Please explain how your statement of fact is true considering that this cited paper is stating that there is such a disease and possibly some portion of that population obesity is a product of this disease.
"Adv36 causes obesity in animals. In humans, Adv36 associates with obesity both in adults and children and the prevalence of Adv36 increases in relation to the body mass index."
Please state how "possibly some portion" is supposed to have any meaning whatsoever.
"A quarter of the entire US population didn't suddenly catch a disease and become obese."
Why not? When you put it that way, it strikes me as pretty implausible that 'a quarter of the entire US population suddenly became lazy and started stuffing their faces for no good reason'. Epidemics have happened frequently before; bouts of mass overeating are historically rare.
Being sedentary and taking in 2500 calories a day is definitely a choice. A very small percentage of obese people have hunger as extreme as your 5 cookie box example. All it takes is not paying attention to caloric intake over a long period like 5 years.