Helen, are you seriously suggesting that an internet discussion board, devoted to folk music, should not permit people to say what they do and don't like about performers, their art and their publicity? Why ever not?
There's no comparison to interrupting a live performance. I could comment on people who walk in and out to the bar/their seats in the middle of songs, which I think very bad manners.
OK, on the net sometimes things are not phrased in the most tactful manner, and perhaps would not be said in quite the same way to the artist face-to-face. I think most of us are grown-up about that, and do make some allowance in what we read.
The bottom line is that a performer is making a public display of himself, and the public are entitled to comment on it.