"But within the folkworld several threads seem to define folk in opposition to the commercial. This maybe some sort of Sharpian/Victorian nostalgia for pre-industrial days of old, or it may be leftish anti-capitalism, or it may be some combination of both."

Why should it be any of that? Folk music and "the commercial" can walk past each other or interact at their edges without confrontation. Opposition could be in the eye of the (often non-performing) beholder...

I could also point out to you that neither Sharp nor the Victorians knew the "pre-industrial days of old" any more than we do.