I agree with what most fellahs have already said:
They should be allowed to do whatever they feel like doing, as long as they don't somehow convince other people to get fat as well. It's their body, their life.
Besides, who exactly would be the brave soul to tell the large, fat people out there to not go eat at fast food places? You fattie-haters (few as you are) out there are pretty lucky this isn't a face-to-face dialogue. You might have been flattened by now.