Well, everybody has their own reasons for literally everything. It all depends on what's happened in the person's life. If someone loses someone, or get's hurt, or something they take out their pain on other people, leading them to kill people.
All of this goes under sociology, behavioral science, criminology, victimology, and psychology.
As for hatred, I don't know that people "love" it. People just have a need to be defiant and rebellious.
As for power, people are sometimes control freaks. They need to be in control of all situations. This has to do with how they were treated as a child. If they were beaten, or bullied, they'd like to rise up and become the beater or the bully.
