ABC News recently had a video on My Yahoo that had the "worst" foods purported to be good for you (alas, I don't have a deep link to the video). First on the list of diet soda. The silly woman said that those who drink diet soda are heavier than those who don't, so you shouldn't drink diet soda.
Uh, newsflash: You've got the cause and the effect backwards there. People who are heavy drink diet soda because they know they're heavy. The ones who aren't heavy drink whatever the hell they want because whatever they're doing is working for them (or at least isn't a problem).
It's like saying bariatric surgery causes obesity because only obese people have it done.