Pre-Holiday Rant

Since I'll have another full day to kill before my holiday begins, I figure I'll do my actual Christmas rant tomorrow. For now, I have another little bit of speculation I'd like to explore.
I've been wondering at the apparently intractable difference between different parts of the political spectrum. People with the same basic goals and information still come up with varying strategies for how to govern. I believe it has something to do with how our social behavior evolved.
There would have been evolutionary pressure on our behavior from a variety of sources. One source of pressure would have been that to co-operate. The more caopable an individual is of knowing and trusting others, and of then including them within the group which they trust, the larger such a group could be and the more advantages from having a large group of allies that individual would have. There would also be an opposing pressure, to be wary of others. This would arise because inevitably there would be individuals who would betray the trust of others. The more wary an individual was, the more able they would be to avoid betrayal.
Each human would be, in effect, his or her own state- they would have allies and enemies and those who sat somewhere in between. No one could be too inclusive because they would leave themselves too open to back-stabbing, but no one come be too suspicious or they would have fewer allies than anyone else and would be unable to defend their interests. Since this behavior would be regulated by a number of different genes, as well as being calibrated by the social environment the person was raised in, any group of people would mark at different points in the spectrum between these extremes. In an overly inclusive society, a person who was a little less inclusive would have the advantage because they would be betrayed less, whereas in an overly exclusive society a slightly more inclusive person would have the advantage of extra allies.
When it comes to political philosophy, these attitudes would map to the right or left-wing attitude of the individual. Inclusive individuals would be on the left side, exclusive too the right. The issue with politics is that people tend to think that if something is good in small amounts, it would be better in large amounts, so they take their political philosophy to extremes. Thus on the far right you have ever more exclusive groups, more racism and class warfare and the belief that only a very select group has any value, whereas on the extreme right you have absurd inclusiveness which ignores even the most valid types of metitocracy and drags everyone down to a low equality within a system of rampant corruption. Just as with the behavior of the indiviudal, the behavior of democratic nations will self-correct over time because the greatest excesses will be punished by the fact that a party that pushes too far to one side will give their more moderate rivals much greater public support.