A book that was recently reviewed in Physics World seems to support what I had said. In Rethinking Expertise by Harry Collins and Robert Evans, the authors makes several distinction on the level of knowledge that a person can have.
The starting point of the book is the obvious realization that, in science or any other specialized field, some people know more than others. To develop this truism, the authors present a “periodic table of expertise” — a classification that will make it clear who we should listen to when there is a decision to be made that includes a technical component. At one end of the scale is what Collins and Evans (who is also a Cardiff sociologist) engagingly call “beer-mat expertise” — that level of knowledge that is needed to answer questions in pub quizzes. Slightly above this lies the knowledge that one might gain from reading serious journalism and popular books about a subject. Further up the scale is the expertise that only comes when one knows the original research papers in a field. Collins and Evans argue that to achieve the highest level of expertise — at which one can make original contributions to a field — one needs to go beyond the written word to the tacit knowledge that is contained in a research community. This is the technical know-how and received wisdom that seep into aspirant scientists during their graduate-student apprenticeship to give them what Collins and Evans call “contributory expertise”.
What Collins and Evans claim as original is their identification of a new type of expertise, which they call “interactional expertise”. People who have this kind of expertise share some of the tacit knowledge of the communities of practitioners while still not having the full set of skills that would allow them to make original contributions to the field. In other words, people with interactional expertise are fluent in the language of the specialism, but not with its practice.
I think most of us who work in science are fully aware of that, and that is why we seldom offer "expert" opinion on an area that we didn't specialize in. We KNOW what level of understanding is required to be able to make an original contribution to it. This is something crackpots are not aware of, and something that most of the public are not aware of when they talk about science and gave the impression that they have actually understood the issue on hand.
I think I have the "interactional expertise" in many areas, where I can actually engage in a semi-intelligent conversation with experts in those areas. However, if someone were to ask me for information about something in those areas, I would definitely refer to an expert, even though I believe that I know more about that area of study more than the average Joe off the street. Unfortunately, for some people, my referral to an expert somehow implied that I'm "scientifically illiterate". How logical is that?