I do agree with your general premise. Most health advice is too complex, and it can all be boiled down to: eat whole foods, mostly veggies. If you must eat processed, the less ingredients the better.

A lot of the confusion also has to do with people treating their diet as religion. Also, there's a lot of misinformation from the government (the normal Food Pyramid is the worst thing to follow if you need to lose weight), and as a result lots of conflict with popular wisdom. As such, when someone gives advice that is different from the norm, people immediately shoot it down as just a fad.