The word fanatic is everywhere. Sports fanatics. Video game fanatics. Political fanatics. Religious fanatics. With so many uses for the word, what exactly does it mean?

The Oxford English Dictionary can help. It provides several senses of the word fanatic. None are flattering. But all are consistent with what we know about fanaticism.

Out of the gate, OED tells us that fanatics are frenzied. In fact, they may even be possessed: “Of an action or speech: Such as might result from possession by a deity or demon; frantic, furious. Of a person: Frenzied, mad.” Fanatics behave so crazily, we’re warned, it’s like they’ve been overtaken by a supernatural force.

And it only gets worse.

OED goes on to say that fanatics are not reasonable. Rather, they are “characterized, influenced, or prompted by excessive and mistaken enthusiasm, esp. in religious matters.” OED does add that sometimes fanatics are visionaries, but cautions that in those rare moments when a fanatic is onto something, their excessive enthusiasm overrides their ability to reason.

On the whole, the OED tells us that fanatics are unreasonable extremists plagued by two character flaws. Their views are extreme, and they are unwilling to consider facts that don’t square with their beliefs. These hardly are traits we would like to see in our friends, family, and our community.

Wrong and Mistaken?

The general idea that fanatics are unreasonable extremists is sometimes traced back to Edmund Burke. Burke was an 18th-century Irish statesman. His opposition to fanaticism was brought out by the violence and chaos of the French Revolution.

Burke believed that when change happened thoughtfully, guided by laws, traditions, and people’s lived experi­ences, the change would be better for everyone.

To voice his oppo­sition to the French Revolution, Burke wrote Reflections on the Revolu­tion in France. Reflections painted France’s revolutionaries as fanatics. As he put it, the revolutionaries had “a certain inward fanatical assur­ance and illumination upon all sub­jects.” Because France’s hardline revolutionaries thought that they were right—and everyone else was wrong—Burke said that they were no better than the hardline French mon­archists that they were trying to overthrow.

To think about this dif­ferently, the revolution­aries thought that most everything in France needed to change, and change right away. The monarchists thought that most everything in France was fine just the way it was, so no change was needed. Neither side was entirely right.

The fact of the matter is that the French Revolution was a complex historical event. Liberal societies such as ours owe the French Revolution a debt of gratitude. It pushed against a corrupt ruling class. And it demanded society be based on ideals of liberty, equality, and fraternity. Many of the “radical” ideals advanced by the French Revolution are now cornerstones of liberal democracy. Yet some aspects of the revolution—such as the Reign of Terror where 16,000 people were killed, or the creation of Temples of Reason for people to worship reason—were horrifying and absurd.

The Good and the Bad

Because Burke portrayed France’s revolutionaries as fanatics—and many of them were—philosopher Alberto Toscano has charged Burke with “set[ting] the template for treating all advocates of radical equality as dangerous fanatics.” This is a fair point. Many radical equality movements that followed the French Revolution—such as slavery abolitionists, labour organisers, suffragettes, and peace activists— were painted by their opponents as fanatical. Yet these “fanatics” were on the right side of history. They helped establish many of today’s liberal democratic norms.

This is why we should carefully use the word fanatic. Not all fanatics are bad. In fact, many people who have been called “fanatics” have helped move society forward. If we carelessly call everyone who we don’t agree with a fanatic, we may fail to learn from them. And we may further polarise society. Values and beliefs should be thoughtfully considered before passing judgment.

This understood, not all ideas are good. History is littered with objectively terrible fanatical movements. Think of Adolf Hitler and the Nazis. Their fanatical drive for a “pure” society ended in genocide and war. The same goes for Joseph Stalin and the Russian Bolsheviks. Stalin’s fanatical quest to achieve communism left 20 million dead.

This is why some fanatical movements are more worrisome than others. There’s nothing wrong with, say, being fanatical about a sports team. Such fanaticism is often in good fun. Even radical political or social movements often have merits. So long as supporters keep their enthusiasm in check, use reason, and respect democratic rules, we can consider them a healthy—if at times uncomfortable—part of society.

But there are times to be concerned. When fanatics interfere with people’s rights, paint fellow members of society as “others,” or propose or actually harm people, we have reason to worry.

Let’s think more about the fanatics that we should concern ourselves with. The coming pages look at some fanatical movements of the 20th century. As you read, ask yourself what would make these movements appealing? Why would otherwise decent people come to support such terrible things? And what could have been done to stop them?