I think the butter thing, like a lot of very specific dietary concerns, is hard to settle popularly because the answer may not be the same for everyone. Carbohydrate intake is another good example of that phenomenon (I hestitate to even call it a "problem"--the problem is the alleged need for a universal answer). A lot of people who live relatively sedentary lifestyles take in a lot more carbs than they use, and might reasonably be advised to cut back. That does not make it good advice for, say, a bike commuter who's actually getting a reasonable amount of cardiovascular exercise.