And dietician's pushed the traditional food pyramid for years, which many current dietician's find fault with, years after nutritionist's pointed out the same thing.
I've met successful doctors, lawyers, trainers, etc., that believe in crazy wild theories that have no basis in anything other than what they want to believe. Success amazingly often has very little to do with if people are right or wrong (I'm sure there are some very wealthy astrologers out there).
By your theory, it doesn't matter which doctor you pick, they are all trained physicians, so they all believe the exact same thing. Need a psychologist, just read Dr. Phil's book, he's board certified. Or don't agree with Dr. Phil, then all psychologist's are bad.