Why average people hate people who are different?

Friend of my friend has a situation. This question has been popping around his head for quite some time. Perhaps, you could help me help him help himself.

Dude has been someone you would call different. Back in the days when we started smoking inbetween school classes, most of us would hold cigarette in our right hand. Not him. Dude was holding it in left and he isn't even left handed. Tho, he has some crazy story to explain himself and why he holds cigarette in his left hand. He used to say that he started making signs on paper, not writing, but signs, when he was about 2.5 years old, but his mother, being controlling the way she is, made him switch to his right hand.

He deeply regrets not being able to go back in time and stay lefthanded. When he says a sentence with that tone, it feels like the action of going back in time and the regret is completely justified in the universe we live in. Like it is not all his fiction and imagination that can throw him in the pits of chaotic thoughts, misguiding him through real life by putting pressure on his fragile bipolar mood levels.

Bipolar doesn't help him solve his problems. He never fully trust himself. Angel and devil are talking at the same time. And that's better. Better than one of them talking and the other one being silent.

So yea, my friend is a genius. Genius after suffered was born when he was 2.5 year old, felt loss and built new self. Not many are able to build themselves based upon the wishes of those who are raising them. That is because it is hard to go through this conversation:

avg human - Why are you so different? (rude)
diff human - I am not. (noble lie)
avg human - Yes you are. What is WRONG in being normal? Like the rest of us. Why do you feel need to be different, aren't we GOOD enough for you?

To all different humans out there that are facing daily dilemmas - say the truth. Stand up for your qualities. Why average people EVENTUALLY hate people who are different? Because hate is an average emotion. Everyone can feel it. That makes it average. I will say that to my friend tomorrow.