Why can't people stop being hyper-nationalistic when cheering?

Please explain why so many people cannot help but engage in "power-tripping" or hyper-nationalistic cheering when supporting a team.
Because of this, when their team happens to win once due to a referee's decision, they act as if they own the world, shouting loudly that everyone else is a fool or that no one is better than them, making it nearly impossible to have a conversation.
Furthermore, even when the opposing team sings "The referees back there are the problem," those with strong nationalistic or superior attitudes just start by snickering, which makes communication even more difficult.