Why do people care so much about political issues?

When I first became politically aware, say, in junior high, I was very conservative. I was curious about the "other" side, though, so I went to college at Berkeley. Since then, I've felt that both sides generally have something worthwhile to say.

In politics, the answers are not clear cut. If they were, then the issues would not be contentious, and therefore they would not be political issues. What I've been wondering about lately is why people believe so strongly in one side or the other of a political issue when the "right" position is (almost by definition) unclear. I can think of a few possibilities:

1. People think they have information that other people do not have (including experiences that others have not had)
   
2. People think they are smarter than the people on the other side (they posess understanding that others are unable to attain)
   
3. People's interests differ, and they are trying to secure benefits for themselves or deny special benefits to others
   

Please note: "Because I'm right and they're wrong" is not a valid answer.