Why do people want to kill others?

Answer 1

It is suggested that there are three reasons 1) mental illness, 2) Abuse 3) Brain Damage or a comination of some or of all of these reasons. I'm inclined to think nature plus nurture has a part to play also.
They may be old enemys

Answer 2

People often want to kill others for a number of reasons:

1. Hate. Because they are haters! They are not happy. They are crazy.

2. Greed. Some kill to get what others have or to collect on their insurance.

3. Jealousy. Maybe they caught a lover cheating or someone they like does not love them back. Maybe a child felt their parents loved another child more.

4. Revenge. Maybe the other person did something to them.

5. Fear or paranoia. Some kill out of fear. One example is gay panic. They are afraid others may think they are gay, so they kill a gay person who was flirting with them. Or they kill someone who is dressed as a member of the other sex and don't discover this until they are in bed together. Or they might kill people they suspect of being terrorists as a preemptive strike.

6. To send a message or force others to comply. Maybe someone owed them a lot of money and are not able to pay it back. So they kill the person to send the message not to mess with the person. Along this line is terrorism. The idea is to drive fear into others.

7. Sadism or the sheer "fun" of it. Some just wonder what it feels like to kill, or they just like to watch others suffer.

8. Developmental trauma. Maybe a certain type of person triggers flashbacks to a time they felt powerless. So they act out against persons who fit that mold. Maybe they hate their mother and kill others who look like their mother. Or maybe a lover rejected them and they want to take it out on all who look like them.

9. Mental illness and substance abuse. A man who was high on meth killed a fellow passenger on a Greyhound bus. He even ate part of the person and walked around carrying their head. When he was arrested, he seemed okay and didn't know what he had just done. A couple years later, he said that he thought the person was an alien and that God was telling him to kill aliens. It also came to light that he was abusing crystal meth at the time he killed the passenger. Women who kill their own children often suffer postpartum depression at the time they do that.

10. No reason at all. Sometimes, particularly with younger people who are violent, there are no discernible motives at all. They just act and cannot tell you why.