Why do we hate others?
There are lots of different reasons why people hate others, but most of the time it is a fear of the unknown. Essentially, we hate people because we are ignorant about them.
Evolutionarily speaking fear of that which we don't know was a survival tactic because we wouldn't often put ourselves in unfamiliar situations that could harm us without approaching with extreme caution. These days though we retain that fear of unknown situations and apply it unnecessarily.
People tend to assume they can read a person's mind. That they can know their motives. That they can know how they feel. That they can know how they think. A lot of the time this causes us to jump to conclusions about another person based solely on the appearance of their actions.
It's simply a biological instinct to proceed with caution when something is different from you. The neighbouring tribe that looks different than yours could threaten your existence. That animal you've never seen before could kill you.
The challenge these days is to overcome our outdated primitive instincts that are no longer necessary in their extreme forms. It is always important to have healthy boundaries protecting us from the potential harm of other people, but these days it isn't always a threat to your life to give people the benefit of the doubt and be the first person to extend a welcoming hand.