"By a purist definition, Woody Guthrie, Pete Seeger, Lead Belly, Bob Dylan, Phil Ochs, Si Kahn, Joe Jencks, Janis Ian, Joni Mitchell, Anne Feeney, Utah Phillips and so many others do not sing folk songs."

I don't actually give a flying fuck what you call them, I do in fact like some of those people's work. But I want for people who set up events where the kind of music I know much more about and actually play is excluded, to be honest enough to tell me they're excluding it so I don't waste an entire evening going to their club or session.

It's very common practice for people into singer-songwriter music to try to keep all other kinds of music out of their venue. The problem isn't exclusivity in verbal definition, it's exclusivity in actual practice, hidden behind the verbal screen of the word "folk".