As a clinician I know that what actually matters is how to help the person sitting in front of me, remembering that science, meal patterns, macronutrients, and physiology, may not always matter the way some study says they could or should in the face of an individual's life and personal preferences. Ultimately, and regardless of what I think is "right" on paper or right for me, my job is to help patients make sustainable changes that in turn lead them towards the healthiest life that they can actually enjoy.
Similarly, as a public health advocate, I know that if there were any amount of education, or a brilliantly crafted public health message, that in turn would effectively drive societal behaviour change we'd have all already changed all of our behaviours. I can also tell you that energies spent on initiatives relegated to personal responsibility, including but not restricted to those promoting one person's diet tribe, pale in importance to energies spent on initiatives relevant to changing the food environment. And there's no shortage of targets that span all dietary dogmas - from advertising to kids, front-of-package health claim reforms, junk food fundraising, the provision of free cooking skills to kids and adults, national school food programs and improvements, tax incentives and disincentives, and more.
All this to say, it's my opinion that these two flawed foci, that there's one best or right way and that personal responsibility will be our salvation, are the two main reasons why we can't have nice things in nutrition and nutrition related public health.