BUT I DONT LIKE TRAD MUSIC PLAYED BY A ROCK BAND , BUT I AM NOT A PURIST.

I didn't say you did, or should, or whatever you're objecting to. Saying a purist might not like it doesn't mean that anyone who doesn't like it is a purist. That's basic logic and semantics. I have no idea if you are a purist or not. You say not, so that's good enough for me.

in my opinion a purist is someone who runs a singers club and refuses to let singers accompany themselves,

Yep, that is a purist. No arguments there.

. . . the sort of people who enjoy telling others you cant do that there here.

Yeah, yeah, you've said that. You also haven't said why you think everyone should run their club according to your rules. You haven't said why a folk singer should expect to get hired in a jazz club. If someone wants to run a club differently than you want to run a club, why does that bother you so? If you have spent time running a folk venue, bravo for you! And thank you! How would you like it if someone got really mad at you because you're not programming "their" kind of music? Would you book a heavy rock band into your folk club?

I had to talk a friend of mine into continuing to run a small concert series that was devoted to traditional music. A non-traditional folk singer came into her place and screamed at her VERY obscenely for half an hour because she told him she wouldn't book him, and why. This was, at the time, one of the very few places in town that focused on traditional music. There were numerous places for him to play, but he felt that any place that said folk music had to automatically book him because he played folk. Before I talked her down, she had decided to stop putting on concerts rather than subject herself to that again.

As I've said many times already in this discussion, it's not about whether or not someone is a purist, but whether or not they're a jerk about it. The same goes for non-purists.