  Global recruitment into radical Islamic movements has spurred renewed
interest in the appeal of political extremism. Is the appeal a rational
response to material conditions or is it the expression of psychological and
personality disorders associated with aggressive behavior, intolerance,
conspiratorial imagination, and paranoia? Empirical answers using surveys have
been limited by lack of access to extremist groups, while field studies have
lacked psychological measures and failed to compare extremists with contrast
groups. We revisit the debate over the appeal of extremism in the U.S. context
by comparing publicly available Twitter messages written by over 355,000
political extremist followers with messages written by non-extremist U.S.
users. Analysis of text-based psychological indicators supports the moral
foundation theory which identifies emotion as a critical factor in determining
political orientation of individuals. Extremist followers also differ from
others in four of the Big Five personality traits.
