Deciding on "expert" seems completely intractable. What if one fellow has spent a decade studying the subject and agrees with 90% of his fellow decade-studiers on 90% of things but the remaining 10% of topics he has views shared by approximately no one. Is he a crank or an expert? What if he's fairly persuasive to layman/politicians and thus is the head of the Bank of England?
Additionally, if a subject matter does not lend itself to experimentation or feedback mechanisms then you can easily have all the experts be consistently wrong for decades due to group think or conformal pressures.
Not to mention that people are often legitimate experts in a field and a leading expert on their own theory, and yet spout palpable nonsense about what supporters of the alternative theory believe to boost the credentials of their own theory.
Heterodox monetary theories are a particularly good example of this...
In this case I think the fellow should be allowed to speak on the topic he studied.
I agree generally in the end you'd have to trust the forum admins to publish some rules and follow them, but that's already the case in any forum. I'm sure some people would like it and some would hate it. It's at least an interesting alternative to the majority of people not knowing what they are talking about but confidently posting as if they do, even if it's just one of the kinds of forums in the mix in the world.
Additionally, if a subject matter does not lend itself to experimentation or feedback mechanisms then you can easily have all the experts be consistently wrong for decades due to group think or conformal pressures.