Here is link to a really awesome article by Jonathan Haidt that specifically looks at the psychology of libertarianism.
Essentially libertarians place very little value on anything of the traditional liberal or conservative moral concerns in favor of a single moral pole, liberty. Liberal morality is based on fairness , care, and conservative morality is based the previous three plus respect for authority, loyalty to in group, and purity.
Haidt traces this to personality traits of being unemotional, for the most part, and not seeing themselves as part of group. Interestingly libertarians only showed a strong emotional reaction when their freedom was impinged upon in any way.
In general terms what is interesting is that moral psychology is not merely on a spectrum between liberal and conservative but looks more like a triangle with three distinct types of moral personalities.