The paper defines an extremist as an individual whose ideal point in the issue space is extreme in some dimension, and a "monomaniac" (no derogatory connotation) as an individual for whom one issue is given more weight, has greater "salience", than the others. This difference in salience is reflected in the spatial theory of voting by indifference curves taking the form of ellipses. Using this theoretical framework, it is showed that monomaniacs, even though they are not necessarily also extremists, can easily be induced by extremist politicians to form or support extremist coalitions. This phenomenon can account for a number of the observed characteristics of extremist movements. It also has implications on the questions of how the results of surveys should be interpreted, of why members or supporters of extremist coalitions can sincerely not feel responsible for some of the deeds of these coalitions, and of what may happen to social judgments of guilt and innocence when the salience of issues, as perceived in retrospect by society, changes in the course of time - as has been the case in postwar France with regard to some aspects of the Vichy regime.