Please Help Me - I do not understand

I consider myself a life long Jets fan. Until I retired and moved out of the country, I was a season ticket holder. Of my two best friends, one is a Pats fan and one is a Fins fan. We get together each Sunday (Monday also if our teams are involved), and act like fans. Calling each other crazy, moaning when our team makes an error, announcing to the world how great our team is, when we make a good play. Since I live in a tourist area we are surrounded by people we do not know, who watch the game with us. There has never been any name calling or personal attacks, but there have been a LOT of derogatory things said about each other's team. But that has always been a part of the fun, The more biting the comment, the bigger the laugh. It is just a game, an entertainment, which if it was not for the harassment of each other, would many times not be worth the time devoted to it (like Monday's Game against the Pats). I had a terrible, yet great time, it was a lot of fun. At the end of the game, I told my friends  I was going home to cry myself to sleep, and instantly  the 2010 official crying towel was born, which I fully expect to give to my Fin's Fan friend this Sunday. But that good natured harassment does not seem to be the rule on these blogs. People attack each other viciously and violently engaging in personal attacks. They want to ban you if you say anything bad about their team, even if it is said in a polite and respectful matter. It seem that you are not talking about a team in a game, but are talking about them, their identity is the team. And this reaction I do not understand.