Disagreement and Doodoo Heads

Here's a problem that I think about all the time. It has troubled me for years.

Some people who disagree with me are doodoo heads and some are not. If a person who disagrees with me is not a doodoo head and I am not a doodoo head, then why do we disagree? What blocks our understanding?

Here are some possible explanations.

-Lying
-Insanity or some kind of self-deception
-Some kind of psychological/physiological difference, perhaps brought on by experience, that effects the ability to perceive or even imagine certain things
-Varying degrees and aspects of doodoo headedness

Does disagreement about the crappyness of the movie Armageddon function the same way as disagreement about the stupidity of Prop 8?

Are my personal dislikes on the same spectrum as my value system? I hope not. I work hard to make it not so. I bristle when people confuse style with politics, or morality with taste.

In many cases, I can safely throw hands up, say, "Those people are stupid ... er...uh...mistaken," and be done with it. But since we're all stuck in this world together, doodoo heads and all, effecting each others lives, I can't throw my hands up as often as I'd like to.