Pip: when this hypothetical folk club was set up, the person doing so must have had an idea of what sort of music they were expecting to attract and what they meant by "folk", or they would not have used that label. Likewise the singer-songwriters presumably also have a notion of "folk", which they consider their songs fall into. People who write songs which they consider to be in other genres are less likely to assume that a folk club is a natural venue for them. So we need, if not a definition, at least an understanding of what is folk, and what is not.

SS, what you described can just as easily be experienced with other musical forms. I have a friend who plays classical music with an amateur orchestra, and that's as much to do with socialising as it is with playing music. I don't see any difference in concept between that and a folk club. Where I do see a difference is that a folk club should present folk music, but you've ruled that out because to you anything played there is de facto folk. So there must be something else which makes it justify the label "folk".

Hardly anyone, with one or two exceptions, is arguing that "folk" should mean only "traditional". That meaning was lost long ago. However, if a song is not traditional then it must have something else which qualifies it to be thought of as "folk". The further a song gets in style and content from traditional idioms, the more difficult it is for me to recognise it as "folk".