I have an increasingly-strong suspicion that there's a dangerous insularity about 'experts' (particularly those that deal with the domain of humans rather than things, e.g. doctors and economists and psychologists and lawyers, as opposed to engineers or mathematicians), insofar as they often only interact with their fellows (who in turn are often all from the same demographic) and thus, very much like police officers, end up existing in a kind of bubble of shared prejudices.
This applies particularly to generalists (like GPs) who seem to grossly overestimate how much they know about issues that belong to the domain of specialists.
They are, after all, human beings.
I can easily imagine how they all get together in med school, all mutually congratulating themselves on how smart they are and how much better they did in their exams than their peers.
It clearly goes to their heads, and causes too many of them to believe they know everything.
This sort of problem has arisen so many times in my life - how the hell do you know when an 'expert' actually knows what they are talking about or not? Having qualifications or prestigious job titles really doesn't mean much in the world as it is (just look at Clarence Thomas and Thomas Alito)