For starters let me state I do not mean all obese people, but those who do not suffer any medical condition that's causes obesity should have to start to work out, or at least do something that helps to curb their obesity. There should be a limit on the amount of fast food they are allowed to receive and have to park farther away then most.
People make their own money and they have their own decisions on what they want to eat. If a person wants to have a Big Mac the government should not say that a person cannot eat just because they don't want their country to get fat. Plus what if that person was treating themselves out just for the day.
It is widely accepted that discrimination for any reason is bad practice and discrimination is outlawed in the United States. Obesity is a medical condition, and if the government were to start discriminating against people on the basis of one medical condition, it not only violates anti-discrimination laws, it opens the door to many other kinds of discrimination and creates a dangerous precedent.