Extremists of the Right and Left (same thing) have much in common with extreme libertarians. What is that? A tenacious attachment to a set of values that defies reality.
Extremists of all stripes find their happiness in an inner world of their own making. They interact with the rest of the world mainly for two reasons: (a) to satisfy basic needs (making a living, having sex, etc.) and (b) to manipulate others (to the extent that they can) in furtherance of their world-views.
The extremist personality seems to contain one or more of these traits: Alexithymia, autism spectrum disorder, lack of empathy (arising from autism spectrum disorder), and even psychopathy. Except for the more pronounced variants of autism, these are not crippling disorders.
To the contrary, such disorders enable an extremist to maintain an emotional distance -- an inner coldness -- and thus to pursue his aims without conscience, even while simulating "normality." The more intelligent, cunning, and socially adaptable the extremist, the more likely he is to accomplish his aims.