Malnutrition should not be a first world problem, but obesity is. This is an epidemic in our children and we all have a responsibility to protect kids who don't yet know how to make the right choices. Yes teach them, give them the tools, but show them by setting a good example as well.
Kids enjoy these foods because they get to experience different foods. With these unhealthy foods, they can learn about what the unhealthy food can do to their hygiene and learn that they should not have any...Only every once in a while they can, and without this lesson, when they get older, they will eat all they can of it!
Part of becoming an adult is learning how to make decisions for one's self. They say there's no better teacher than experience, it's easier to loose weight as a child than it is as an adult. Plus, it's not as if they'll be allowed ten ice cream sandwiches a day, I don't think one junk food item each school day will effect their health. Adults can't be control freaks and then wonder why children have trouble making their own choices.