That's a whole different thing from the question of unwanted musical or vocal accompaniment.

If people don't quieten down and listen to a singer who is not that loud or who is not that confident, that is not within my definition of a "friendly atmosphere."

Control freaks can screw up a club or a session. But so can bad-mannered oafs who don't care about music and other people. Wanting to hear nothing but the sound of their own voice isn't limited to singers - it's more typical of the loudmouths who prop up the bar in some places.

I think there's a difference between two situations - one is where a bar that is primarily a talking socialising place is tolerant about having a few musicians in the corner. The other is where there is a full-fledged session, and most people are listening. In the first case it's unfair to expect quiet, so you just have to bellow a bit. But the second case quiet for songs is good manners and to be expected of anyone with good manners.