The Competitive Nature of Humans
Life itself is competitive. Life fights to survive. Replicating cells thrive to form new versions of itself in evolution and mutation. For billions of years here on Earth life finds a way to live again and again. This competition to survive breeds a kill or be killed mentality. The killing has been manifested for millennia in many different ways: plants, animals...humans.
Homo sapiens are the most successful fighting survivors in Earth's known history. We evolved to be hunter gatherers, competing against animals and other humans. Around 100,000 years ago Homo sapiens climbed to the top of the global food chain. In short, we humans have competitive genetic instincts. The fight is simply built into our being.
This explains why, here in the modern age, we continually look to compete. We compete for jobs, for our mates, for our lives. Humans are constantly trying to either keep up with the Jones' or to simply better them.
Even when there is no immediate threat for survival, humans through the ages have culturally sought out a good fight. Humans enjoy competitive games. The ancient Colosseum in Rome is good example of human on human and human on animal competition.
Coke v. Pepsi, Dallas Cowboys vs. Pittsburgh Steelers, Democrat vs. Republican, etc. It is a form of entertainment. People desire to be on the winning team. People demand that they are right and correct. People even die for their opinions, teams, etc. Have you ever witnessed how humans will argue over the stupidest topics? Apple versus Droid is a good example of that. People simply want to compete, argue, and bitch. It's in our nature.