Unless an obese person has specific physical problems that cause their obesity (a very small portion of the population), it is their choice to be obese (I have been morbidly obese, so I know something about this). Obesity causes a great number of physical (and emotional) problems, and taxpayers end up paying for the extra medical attention they have dug themselves into.
Yes, they should have to pay higher insurance rates. Why should people with healthy habits underwrite the medical problems of the obese?
There would be an uproar, but I think we can see a turnaround in the eating habits of Americans, a lowering for the need of medical attention, and a healthier nation.