"when I go somewhere to perform, it is by invitation from someone else ... When I go to a singaround it is because I choose to myself. "

I understand the distinction you are making, but I think its a false one. In my opinion, in both cases you owe the same 'duty of care' to the people you're singing for to sing the song to the best of your ability. Whether they're lined up in rows looking at a stage or gathered informally in a back room shouldn't matter.