A good rule of thumb for being a fan of anything is to support your favorite artist/company/group by spreading the love and not the hate. Ten years ago when internet and social media was not as prominently used, I don't think the term "flame war" was coined yet for feuds between groups of fans or individuals. I would say flaming and flamers have gotten worse over the years and many people have fallen victim to it. If you go on to any youtube page and look at the comments, chances are you'll come across a lot of crap. College humor accurately portrays this in the following video.
Bias is within every individual and we tend to take sides. In schools of America, we are taught to embrace diversity and unconsciously we tend to berate those that conform to a standard. Occasionally we take a neutral stance if stakes get too high. It is not wrong to have your own opinion and nor is it wrong to align yourself with a mainstream idea. Some fans have a tendency to take it too far to express themselves and end up hurting other fans either through the Internet or physically.
Here are some things I've been seeing on Youtube when I browse through visual kei rock PVs that get on my nerves.