What is extremism? The word means advocacy of extreme measures or views. Consider a few examples of extreme measures or views.
A commitment to never lie is an extreme view of honesty. (Extreme consistency in a virtue)
Taking a larger than normal dose of a medicine is an extreme measure. (Extreme with respect to a norm)
There is nothing in the word itself that indicates either a positive or negative evaluation. Yet it is almost exclusively used with implicit negative connotations (impracticality, violence, terrorism). Why has the word acquired these connotations and what is the effect?
Consider the effects first. The negative connotations make it possible to reject consistent ideas or actions as impractical by simply labeling them as extremist. The fact that the connotations are implicit allows the person doing the labeling to avoid analyzing the ideas or actions and actually demonstrating or arguing their impracticality. Even worse, it allows the defense of bad ideas. When someone points out the inconsistency in an idea, it suffices to say “Don’t go to extremes.”
Now some of the causes. The dominant philosophy in today’s culture is pragmatism. After decades of unsuccessful attempts to implement vicious principles, the dominant conclusion today is not that the principles were vicious but that principles as such are inapplicable (Ironically this is also an extreme position). Having rejected principles, a pragmatist has no reliable way to project the long-term consequences of his actions. Hence the fear of anything extreme, anything that deviates from the norm, anything that is fully consistent.
Language is a tool of thought. One forms words or concepts to organize one’s thoughts, to concretize, retain and communicate them. A valid concept is an integration of essential similarities. Concepts like extremism that are an integration of inessentials are not just useless. They are destructive. Since one thinks in terms of concepts one has already formed, forming such concepts ensures sloppy thinking.