Just because WalkaboutsVerse said it, it doesn't mean it's wrong.

It's not what he says that's the problem, rather the way he says it, turning a basic notion of universal musical practise - i.e. vernacular monophonic modality - into part of an absolutist cultural manifesto, wherein all things serve a central agenda of an ethnically cleansed English National Culture.

There is no right here, but there are plenty of wrongs, along with any amount of opinions on what might have been and why that might have been the case. All of which is very interesting of course, but about the only thing we can prove is that there are no rules, and that whatever we might think about something, there'll always be someone else thinking about it differently.

He has a right to say such things; but in so doing people have a right to advise him how seriously off the mark he is - not out of any personal malice (for example, I would never offer the sort of critical damnation of his work as you do in your opening sentence!) but in the hope that he might take some of it on board and see the error of his ways - not just in his thinking about Folk Music, but his whole self-published & self-publicised philosophy of life.   

Given that, I think Mudcat gives him a very fair hearing indeed.