There’s been a lot of tutting-tutting about the people who are overreacting to the Ebola virus. There was the lady who showed up at the airport in a homemade hazmat suit. There were the hundreds of parents in Mississippi who pulled their kids from school because the principal had traveled to Zambia, a country in southern Africa untouched by the Ebola outbreak in the Western region of the continent. There was the school district in Ohio that closed a middle school and an elementary school because an employee might have flown on the same plane (not even the same flight) as an Ebola-infected health care worker.

The critics point out that these people are behaving hysterically, all out of proportion to the scientific risks, which, of course, is true. But the critics misunderstand what’s going on here. Fear isn’t only a function of risk; it’s a function of isolation. We live in a society almost perfectly suited for contagions of hysteria and overreaction.

In the first place, we’re living in a segmented society. Over the past few decades we’ve seen a pervasive increase in the gaps between different social classes. People are much less likely to marry across social class, or to join a club and befriend people across social class.

That means there are many more people who feel completely alienated from the leadership class of this country, whether it’s the political, cultural or scientific leadership. They don’t know people in authority. They perceive a vast status gap between themselves and people in authority. They may harbor feelings of intellectual inferiority toward people in authority. It becomes easy to wave away the whole lot of them, and that distrust isolates them further. “What loneliness is more lonely than distrust,” George Eliot writes in “Middlemarch.”So you get the rise of the anti-vaccine parents, who simply distrust the cloud of experts telling them that vaccines are safe for their children. You get the rise of the anti-science folks, who distrust the realm of far-off studies and prefer anecdotes from friends to data about populations. You get more and more people who simply do not believe what the establishment is telling them about the Ebola virus, especially since the establishment doesn’t seem particularly competent anyway.

Second, you’ve got a large group of people who are bone-deep suspicious of globalization, what it does to their jobs and their communities. Along comes Ebola, which is the perfect biological embodiment of what many fear about globalization. It is a dark insidious force from a mysterious place far away that seems to be able to spread uncontrollably and get into the intimate spheres of life back home.

Third, you’ve got the culture of instant news. It’s a weird phenomenon of the media age that, except in extreme circumstances, it is a lot scarier to follow an event on TV than it is to actually be there covering it. When you’re watching on TV, you only see the death and mayhem. But when you’re actually there, you see the broader context of everyday life going on alongside. Studies of the Boston Marathon bombing found that people who consumed a lot of news media during the first week suffered more stress than people who were actually there.

Fourth, you’ve got our culture’s tendency to distance itself from death. Philip Roth once wrote: “In every calm and reasonable person there is a hidden second person scared witless about death.” In cultures where death is more present, or at least dealt with more commonly, people are more familiar with that second person, and people can think a bit more clearly about risks of death in any given moment.

In cultures where people deal with death by simply getting it out of their minds, the prospect of sudden savage death, even if extremely unlikely, can arouse a mental fog of fear, and an unmoored and utopian desire to want to reduce the risk of early death to zero, all other considerations be damned.

Given all these conditions, you wind up with an emotional spiral that develops its own momentum.

The Ebola crisis has aroused its own flavor of fear. It’s not the heart-pounding fear you might feel if you were running away from a bear or some distinct threat. It’s a sour, existential fear. It’s a fear you feel when the whole environment seems hostile, when the things that are supposed to keep you safe, like national borders and national authorities, seem porous and ineffective, when some menace is hard to understand.

In these circumstances, skepticism about authority turns into corrosive cynicism. People seek to build walls, to pull in the circle of trust. They become afraid. Fear, of course, breeds fear. Fear is a fog that alters perception and clouds thought. Fear is, in the novelist Yann Martel’s words, “a wordless darkness.”Ebola is a treacherous adversary. It’s found a weakness in our bodies. Worse, it exploits the weakness in the fabric our culture.