I don't generally care either way about joining in. When new to the folk scene I used to think it seemed a bit rude, now I accept it as a part of folkie culture. Sometimes though I would definitely rather hear an individual do their thing, rather than a crowd, otherwise everything starts to sound alike. As to 'gatekeepers', if I ran a club (which I don't) I'd definitely encourage people to at least make an effort to practice their instrument and the pieces they want to perform, rather than turning up and saying "I've never sung this before" "I haven't played this for twenty years". Folk is the only place I've noticed this to happen. In Am Dram people learn their lines. In Poetry Slams people don't take semi worked out ideas to the platform. In Choral singing, you practice till it's right before performing. In Open Mics performers learn their pieces first. I don't know where the 'good enough for folk' thing came from, but it definitely exists. Some think that's a good thing I suppose and they have every right to such an opinion of course, but I guess I must be Hitler ;-)