Will and Vic are saying that some people join in badly.

No - I quoted a particular occasion when the percussion accompaniment was a little top-heavy. I also said that that was the way it was and I accepted it.

At the sessions I run and help to run, all are welcome to join in with anything, unless the instigator of the song/tune indicates otherwise.

As for myself as instigator, I'm happy for everyone who wants to to join in - slightly irritating as it might be sometimes - because I believe that's what my "session" is for: to bring people of all types, abilities and persuasions together to make communal music. The result of that can occasionally be tedious - it can also occasionally be glorious.