People who would never think they were capable of comment on, say, nuclear reactor design with an hours study never the less think they're qualified to talk about the health effects of xyz based on about as much.

Much as doctors, who know jack shit about statistical and causal inference, or risk analysis, consider themselves not only qualified to make claims in those domains, but consider their ill informed opinions the Word of God, which it is blasphemy to question.

Probably because it's so very very common and almost always utter bollocks.

I suggest that they're using a poor reference set.

There are plenty of people here who know much more than jack shit about statistical and causal inference, and those have usually been the grounds of the criticism here of the generally accepted medical analysis.