is too much hate on both sides. I have noticed that hatred occurs most strongly in younger sports fans - I think immaturity plays a big role.
I think the better question for this board is: "Why do active LDS BYU fans go against the counsel of church leaders and spew hatred for Utah?" There is tons of Utah hate on this board. I think the answer will provide the answer to the question in the original post. It is not an easy question.
BTW I think message boards in general attract haters and people that aren't haters in public will be haters anonymously. The BYU fans and students that are my friends show very little hatred for Utah; and I think most people are that way.