I believe that while many, many people are intellectually aware of how unhealthy soda and processed meat and other foods of the like are [even when the information is frightening], the addiction to the product continues and eventually the consumer grows jaded and apathetic about the dangers [not only from the chemicals in the foods, but from the constant slamming exposure of these products being used/eaten.. from Television, movies, magazines, peers, friends and family, ect.].
It seems the common media messages connect these foods to feelings of having fun [emotional conditioning through laughter, smiling, a carefree attitude], security [a stable home, family, friends], acceptance and whatnot.