Why Do We Hate?

As I have been very sick the last couple of days I have had a lot of time to reflect on the Lord of the Rings Trilogy. What I can't understand is why the Elves and the Dwarfs hate each other so much. I mean really? You would think an enlightened immortal group of people who love nature and spend most of their time in the trees would have no qualms with a people who love rocks and spend all of their time underground. Why can't they just be happy in their own spheres of influence? ...wow I am really sick... :)