I am really, really trying to figure out why people divide along right/left lines. What follows is an idea of mine (still taking shape)...
I think it may be linked, in a way, to ADD. There is a theory of Thom Hartmann's (which makes sense to me, having been diagnosed with ADD at 40) that people with so-called ADD are hard-wired with 'hunter' characteristics, meaning they are flexible and easily distracted, so that if an animal comes by, they can drop everything and chase it. They constantly scan their environment and are always active, alert and ready with a pump of adrenaline so that they can go after their prey (read:hyperactive). They have to be risk-takers to catch animals. They are loners, adventurous and easily bored. The other, non-ADD types are hardwired with 'farmer' characteristics, which requires a completely different type of mentality. A farmer has to be always conscious of time, schedule and routine; if they are not aware of the proper times for planting, for instance, their crops will not grow and therefore they will not survive. Steadiness, patience and concentration are key for farmers. But if they had to live in a hunter's world, the characteristics that help them survive as farmers would doom them in the hunter's world. Their animal does not come at a specific time.
The theory is that Americans are more ADD than Europe because the kind of people who would leave the only world they knew to go someplace completely unknown for a chance of something better would be the ADD or 'hunter' types; therefore we as a nation have a larger percentage of people who exhibit those traits which are labeled ADD. However, our society is structured for 'farmers'. So you have the right-wing, or conservatives (this is a very broad generalization, with plenty of gradations) who are 'farmers'; they value teamwork, organization, conservation, hierarchy, authority, dependability and structure - all necessary traits for farmer survival. Then you have the left-wing, or liberals, who often fall into the 'hunter' category; they value independence, autonomy, individualism, exploration, innovation, creativity, alternate solutions instead of the 'status quo', hyperactivity and hyper-focus when locked in on something. These are necessary traits for hunter survival.
Now, obviously very few people are completely one way or the other; most people are a mixture of the two, but people do tend to preponderate towards one or the other. That's why really ADD people have a hard time functioning in this farmer society, starting with school and going on from there.
But I think that this is one of the roots of prejudice, and the reason we tend to divide up among party lines. For instance, I was talking to a conservative friend, a very intelligent guy, the other day, hoping to get some insight into his mental processes - why he and I, who have the same access to the same basic set of facts, see things so differently. We're both in agreement about basic values - personal responsibility, family, honesty and so forth. But what was interesting was when we began to dance around the subject of welfare. I mentioned that a friend of my husband's was disabled and on Social Security. He was immediately disparaging about her being 'on the dole'. Now, we both have valid points on this issue. There are people who take advantage of welfare. There are also people for whom there is no other option. Somewhere in between is the truth, but I go to the place of the people who are needy and deserving of help, and he goes to the place of the lazy free-loader. Both are true. But statistics (or as Mark Twain put it, 'lies, damned lies, and statistics') can be so easily manipulated that finding the real ratio of free-loaders to needy recipients is next to impossible.
I think we make these judgments based on our hard-wiring, and assemble the available data to fit our worldview. The right values financial and business freedom and sees it as paramount to society, as a farmer would need to in order to survive. And the left values individual and personal freedom and does not care for authority - these are traits a hunter needs in order to survive in his environment.
When it really comes down to it, it's all a 'belief system'. Every bit of 'news' and 'information' we get is something we have to take on faith, unless we can be everywhere at once, see everything first-hand, and correlate it all. So we have to make decisions about whose pronouncements we have faith in. It's not about believing in God at all, but believing what people say, and which people are saying it, and why they are saying it. And there is such a barrage of 'information' out there that one can take one's pick of anything that suits one's own particular mindset. Even science is taken on faith; that the work of the scientists that precede us is accurate. There is simply too much information floating around for an individual to process it all.
Now, I'm not saying that all liberals have ADD, or that all conservatives are plodding farmers. But I am positing that how we interpret the world may depend on the set of filters and wiring that are a part of our innate personality types. Liberals will say that Bill Clinton was responsible for the relative peace and prosperity of his presidency. A conservative will say that it was because of the Republican Congress in place at the time. It might be neither, or both, or have nothing to do with anything political at all. But our individual filters will skew it one way or the other.
So I think prejudice itself stems from our reactions one way or the other based upon whether we are comfortable with hierarchy and structure, or find it oppressive and confining, and that just may be a result of two very different evolutionary survival mechanisms.
Of course, that's just my opinion.