Why is a majority of the world jerks?

It seems like the average people in the world are *******. I mean I’m not saying everyone is a serial killer or pedophile but most people you encounter are rude, aggressive, impatient, self-centered and love to make fun of or talk down to people both in real life and on the internet. I try my best to be nice to everyone and I don’t understand why most people are just horrible. Even here on Yahoo Answers; you get people who don’t want to help; they just want to demean or chastise. Why is the human race so flawed? Maybe it’s better if we go extinct.