Russ Roberts interviews Bryan Caplan. The overall theme is the arguments about socialism. For example, why has socialism produced evil leaders? Is it power that corrupts? Is it that the contest for power selects ruthless individuals? Or is it that socialist ideologues are "born bad" (have personality disorders). Bryan seems to make the case for the latter.
As I recall, Eric Hoffer's "The True Believer" argues that political zealots are people who are have transformed their personal emotional problems into a political agenda. (Or maybe that was my father's gloss on Hoffer.) That is consistent with the "born bad" model of political extremism.