I'm not sure that I use the term, but there are contexts that are suitable for being a purist and contexts that aren't.
E.g.
If I'm calling at a dance club I will try to emphasise the pleasures of dancing in time to the music, and using correct moves.
If I'm describing/demonstrating a 'Strip the Willow' at a wedding ceilidh I end up by saying that variations, deliberate or accidental, are fine as long as you end up at the bottom of the set with your partner.

Folk is meant to be a pleasure, and as you learn more you get that pleasure in different ways. Romping at a ceilidh; dancing a complicated dance at a festival with a roomful of experts; joining in and raising the roof on a simple tune or chorus song; listening to someone making their fiddle sing. It's the FOLK you do it with that make it what it is, so I suppose the term I'd use as perjorative would be 'exclusive'.