It's a general known assumption that when you get a lot of music fans together in one place, they talk. They talk about the bands they love and obsess over. They talk about the bands they never want to hear of again. Internet message boards have become a prime place to do this discussion. It allows many people from all around the world to gather at one forum.
The internet is a fairly safe place to talk about stuff. You don't see anyone face to face, therefore opinions come off stronger and more harsh than many people are used to. Sarcasm often gets lost in the monotony. People are online are generally elitists, too. They have the mentality that no one's opinion matters or is right but thier own. Mix it all together and you're going to get (along with good, informative, and healthy discussion) some crap.
Unfortunately, it's not just music fans who have access to these boards. Any person in a band with internet connection can read it, too. This are fine until someone posts something negative or sarcastic about that certain band. Being online, everything comes off stronger and more cutting. Some bands are good at shrugging it off, however, many take it as a personal insult. Even if there is a whole thread full of praises, the one post saying something negative will be focused on.
The bands who get upset have different ways of handling it. One creative approach was taken by Zao. They wrote a song called "Trashcan Hands" which actually mentioned the screen names of two of the worst offenders. The song was based around the general theme that "who are we to judge them?"
Others actually try to post rebutals. When they only correct facts and keep cool, it turns out fairly productive. However, most cross the line between correcting fact and arguing opinion. When a member of a band posts something that argues someone else's opinion it always comes off as heated and angery. They also sound defensive and weak for being unable to take the negative comments.
One of the members of a well-liked and fairly popular band actually emailed me because of a number of posts I had made about my distaste of their music. He said, amoung other things, "You must really hate us" and wanted to know why. He thought we should "talk things through." Ok.
Bands can't be stopped from reading or posting on message boards. They need to, however, realize that everyone has an opinion and are free to express it. As a band, people look up to them and they have a responcibility to keep thier cool and not start flame wars.