"....appears to be mainly for folk music as enshrined in songs."
Sorry Will; not the case.
I can, (and still would if I had the energy) go out five nights out of seven and hear music ranging from not bad to to world class, all within a twenty minute walk from here, much of it being played by the youngsters still in their teens and early twenties who are still emerging onto the scene.
We sat in a pub in the next village last Wednesday and enjoyed a magic night of fiddle playing from Kevin Burke and Tim O'Brien, with a handful of excellently performed American traditional songs thrown in for good measure.
We were a little late leaving, so we couldn't get into the Jackie Daly session in our local pub, but we can see him any two nights of the week.
I shudder to think what would have happened if somebody had pulled out a fiddle (or even worse, a bodhran) and joined in with Kevin and Tim - there aren't enough trees around here for an impromptu lynching so I suppose the Atlantic would have had to suffice.
How can anybody justify joining in with any performer, singer or musician, without being invited to do so - or does a 'class system' operate which allows it with some and not with others?
I know of several performers who visit the UK regularly as performers and are appalled at the practice, but are too polite to mention it.
By the way Steve, you can't complain about "those who try to change the tempo once somebody has started a tune" if you are going to allow joining in when the audience feels like it unless you issue a rule book of dos and don'ts.
I've said it before, but Walter Pardon felt it necessary to drop two of his favourite songs from his club performance repertoire because of audiences tendencies to harmonise and to slow down the choruses -"made them sound like bloomin' funeral hymns".
He would never in a thousand years have brought himself round to asking them not to.
Jim Carroll