Why do Indian fans gang up on supporters of other teams?

It's completely ridiculous how Indian fans thumbs down dissenting opinions into oblivion.It's completely ok for them to rant about Sachin Tendulkar's greatness or how Harbajan is the best spinner in the world.Not only this but Indian fans repeatedly use abusive language for players of other teams.I don't know why the indian supporters are so overconfident and rude at the same time.