Hear hear, Ella.I was beginning to think that I must be missing something. I twang a guitar and sing. I enjoy joining in with tunes when its appropriate, I enjoy joining in with songs, ditto, and I love it when pepole join in with my stuff, when its appropriate.
The sessions I go to (and there are probably enough in my neck of the woods to go out every night) all reflect this inclusiveness. Occasionally somebody gets it wrong, like when I was tapping in time with a song and got moaned at by the singer, or a fiddle player was overwhelmed by a couple of box players, but tolerance prevails.
The only slight grumble, heard occasionally, is that the instrumentalists get a bit cheesed if they are outnumbered and therefore have to wait a little longer before they get a chance for another set of tunes, but generally speaking people (participants and 'audience') are there to enjoy the music, whatever. And, whoever is 'running' the session - i.e. giving the nod to the next person to play or sing - is sensitive to the needs of the whole gathering so that everybody has a good night out.
Or maybe I am missing something! (I would have put 'am' in italics if I'd known how!)