"I have not resorted to being insulting"
I find being patronised as insulting as anything I have siad - especially;y when you have repeated it as much as you have.
I may be wrong in what I say but I do have some experience in the subject.
Steve.
"Songs written by folk singers"
Which "folk singers" - if the term "folk" has lost its meaning on the club scene, then so has the term folk singer.
"the people who are not part of the sophisticated folk scene."
Depends what you mean - if you are talking about the general public who are no way involved in music and no nothing about it, it would be as insane to include their view of it into any definition.
If you are referring to the older generation of singers who are not part of the scene, it is our experience that they regarded folk songs as something apart from other types of songs they were aware of and often sang, though the terms they used were not necessarily those we use.   
Persnally, I find "there is a delicious irony in some people's refusal to accept that one", or even refer to it.
I have no interest in what either the media or Tin Pan Alley has to say about folk song unless it comes with some knowledge and understanding of the subject - ignorance or self-interest should never be a factor in defining something.
I think there is a great deal to be said of your following list, which are largely parodies, but I, like you, wonder if they have survived.
"Folk' music is a style, plain and simple."
No it isn't, why should it be?
National styles of performance vary wildly, once you start to cross borders they can become totally unrelated to one another.
People here are talking about 'Electric folk' - a thousand miles from the solo, unaccompanied voice that is the norm of folk music of the British Isles - that is the form in which we were introduced to folk song.
If a song is performed on operatic style it remains a folk song performed in operatic style.
George Butterworth's 'Banks of Green Willow', Delius's 'Unto Brig Fair and Vaughan Williams' Sea Symphony No. 4 all use orchestrated folk songs, the styles no way resemble those that introduced us to the songs.
Peter Pears rendition of Britten's 'Lyke Wake Dirge' is a folk ballad sung in operatic style.
You can perform an operatic aria or a Schubert song or a pop song or a Country and Western number or a Lieder composition in a recognised folk style without any of them becoming folk songs.
The researched and well-established definitions you have been given all refer to the origins and transmission of folk songs - you want proof - call round sometime and I'll pull down a hundred or so books and journals dating from over a century ago to the present day - you have yet to provide one.
You talk about "experts" yet refer to non-involved people in the street.   
Sorry, not convinced in the slightest.
Jim Carroll