Looking at the "process" rather than the "content" of this thread for a moment, let me put aside the question of "WHAT is folk", and speak to the question of "WHY try to define folk" (or any other category, or word)?
Some possible motivations behind the debate could include - (1) for the philosophical challenge of thinking about ideas
(2) for the fun & interest of the debate
(3) for practical purposes, e.g. to define boundaries, set up guidelines, etc.
(4) to identify group membership around the category
For the purposes of (1)&(2), philosophical challenge & debate, the more ideas, the better ... in brainstorming, no idea is too outrageous to be interesting ... the more diverse the opinions expressed, the more productive the debate.
On the other hand, for the purposes of (3)&(4), defining boundaries and generating group identity, some *consensus* is needed. And the consensus does not need to be "philosophically correct", as long as it is "practically useful".
This thread certainly meets the needs of (1) & (2) - reflection and debate.
So what about (3) & (4)? Is there a NEED for defined boundaries? Clearly in some circumstances there is. For example, a database with NO restrictions as to content could become so large that it could run out of server space - cost too much to maintain - & take too long to access or search through! A discussion forum with no defining limits could take so long to scan, that people would stop participating because of the sheer volume of correspondence. Arguments in favour of more rigidly defining this forum, also address the need to keep "a space of our own", along the lines of "the rock/country/musicals/etc crowds have other sites, let's keep this separate".
But I am not convinced that any of these are really serious concerns at this point. Computer technology being what it is, I've searched much larger databases without noticing much time difference in the response. And I agree with the approach that if a thread doesn't interest me, I just don't click on it. I certainly *don't* like the idea of flaming someone who posts a thread that someone else thinks is inappropriate, particularly in the absence of posted guidelines as to what the boundaries of the discussion forum are supposed to be. And if I'm preparing a songsheet, & need a song, I don't want to be afraid to post a title in case it's the wrong category & I get reprimanded. Anyway if somewhere wants to reply to a non-folk thread, who is hurt? It seems to me far more likely that non-folk-buffs who find this site friendly, will stay & learn about folk music; and not very likely that that they will *infiltrate & take over* & we'll be left with nothing but Rolling Stones & Led Zeppelin lyrics (or whatever).
My general experience in life is that if a group is friendly & welcoming, new members are very willing to conform to the group norms ... vs. if a group is restrictive & rejecting, potential new members are scared away. I would rather err on the side of inclusiveness than exclusiveness. (At least until the server space runs out.) FWIW -