I don't see the point in continuing to bicker about the way things are done in different areas/countries. These may or may not always have been as they are now, but anyone attending a club or session has to look at what is happening there now, and accept the unwritten rules that are now applied.

Good manners (which apply wherever you are) would suggest that you watch what others do and take your cue from them; you can also pick up clues from whoever is leading a song or tune (or acting as MC if there is one) as to what's expected or encouraged. Good manners should also take care of the one-off problems such as private noodling between tunes, or correcting or shouting down a singer who comes up with a different version of a song.

I do remember one time when I was singing, a bass player who'd never been to our session before played a quiet accompaniment to my song. I didn't mind a bit, but one of our regulars told him off afterwards, in front of everyone else, saying that this was not done. I was really cross, and apologised to the guy at the bar, but he never came back to that session. The bad manners, in this case, was the public criticism of this guy's attemps to join in. If anyone had a problem with it, a private word afterwards would have been enough.

It's all about respecting the musicians/singers and the music they're putting across. In some areas it's evidently considered disrepectful to join in; in others, participation is welcomed and seen as a sign of your appreciation and engagement with the music.

You can enjoy one system more than the other, but that doesn't make either of them wrong or offensive. What is wrong is trying to impose or insist on a uniform etiquette across country and cultural boundaries, or sneer at the way some people choose to enjoy their music.

Marje