Suibhne Astray said I've met many self-confessed Purists who didn't come close; then I've met some seriously qualified people whose encyclopedic knowledge of Traditional Music was matched only by their love of it yet were not purist in the slightest. . . . The people who really know about this stuff always take a wider picture.

Yes, that's pretty much the point I was making in my original post. What I think I failed to make clear is that there ought to be another name for those people who get called "Purists" because - as you say - they usually lack the knowledge on which to base a justifiable stand - which is what I think Leadfingers said about his experience with jazz. Expecting to hear folk in a folk club doesn't make you a "purist", just someone who is likely to be regularly disappointed!