This I argue is a myth, but only in a special case: when it involves a new paradigm. If a conceptual framework is settled, then a professional or mainstream science analysis is appropriate. For example if the topic is “the experimental data on the human reward system” then a cognitive neuroscientist is the one to turn to for analysis and information.
However if framework is unsettled — i.e. a new paradigm — it is open to amateurs as well.
For example, consider the question “how does the (conscious and unconscious) mind connect to the brain?” This is a very basic question which underlies the whole point of cognitive neuroscience. Can any cognitive neuroscientist answer this question? No, absolutely not. Especially when it comes to a specific example, such as “what does the brain do during the movement & state of mind “reach for my phone to type a text.”
These are highly-skilled professionals who do valuable work and know their subject matter. But they are, I would argue, not much closer to understanding the mind/brain connection than Donald Hebb 70 years ago.
Of course, answering this question DOES require knowledge of the subject. But the topic is so broad, philosophical and multi-disciplinary that amateurs can also have a say. Not only that, one could argue knowledge is actually an impediment due to current underlying philosophical assumptions. For example, it is often assumed the mind isn’t very important; and that a clear, realistic and detailed understanding of the mind isn’t necessary to understand the brain. This may or may not be true. But one thing is certain: one needs to be able to SET ASIDE this assumption, in order to take an objective look at the (mind/brain) system.
In short, paradigm shifts in brain science are accessible to professionals and amateurs alike.