In most circumstances, people hate each other because of the difference in perception or interest. Other hate out of the reasons of competition and the social differences. It all varies from one individual to the other.
Some believe that if you're not like them, if you don't share their views and opinions, that something must be wrong with you. It's our differences that make us great, it would be a very boring world if we were all the same. Don't waste your time on the ones who don't like you, instead, concentrate your efforts on those who do.