No I'm not looking to attack anyone (though I may have been known to defend myself vigorously when attacked!).
I think a more interesting question than "what is folk", is why you want to/need to define "folky" music in a particular way. What is the purpose of your definition.
Jim's post above does an excellent job in explaining why he thinks it is important to have very clear terms and derfinitions.....I would say (and I'm sure he will tell me if I'm wrong), from a scholarly, academic point of view (and I'm not accusing him of being a museum curator) I get his point.
I come form a slightly different (probably less pure) place than this. Most of my activities are involved in "selling" (with a small S) folky music to people in my role as a Folk Club Organiser (KFFC) and as my wife's (Wendy Arrowsmith) unpaid agent.
Both of these endeavorers involve packaging a mixture of traditional, self penned and interpretations of other peoples songs into something that "people" want to see/ buy. I need a handy (if academically incorrect)label for this....hence my use of the word folk. To call it anything else would confuse my market places even more than using this term.
Just a thought what do you call your vacuum cleaner? I bet you call it a hoover even if it is not?