People are mean cause they've experienced meanness around them. Plain and simple. You have to learn it somehow. The above seems most clear. The below is confused exposition. There are a lot of different forms of that. An interesting one is where neither party is _trying_ to be mean, but is completely unaware of the situation of the other party, and does things that hurt them. Wars have been fought over such things. Another funny one is where people learn to act friendly in ways others consider mean. But the common one is where your life is all messed up cause people are mean to you, and so you learn to act mean to others as a norm. Do what works! Often people believe here that they are reducing the meanness of others by making it unpleasant to engage in, but demonstrating by their own actions that the result tends to be defensive aggression rather than submission. I put "being hired as a mercenary" and "being mind controlled to mess your community up" both within the category of "your life is all messed up so you learn to act mean to others", but I've heard some would disagree and enjoy their job. Conspiracy theory: people are mean because it prevents them from revolting against the current norms. Aristocrats are tired of being beheaded. Get everybody upset early, when they don't understand they're being oppressed, and then the people who filter through learn no to act aggressively once they do. Further conspiracy theory: Nobody is really acting mean, it's just a bunch of oppressive influences and AIs making them sound mean to keep the hackers from communicating with each other.