(Kacper Pempel/Reuters)

My Wednesday column about “The Americans” triggered a strange onslaught from angry social media leftists defending the Soviet Union. Before yesterday, if had you asked me what fraction of the left still thought the Soviet Union had the right of things, my answer would have been 0.0%. Yet I was informed that their numbers are large enough for this group to have been given a name: “Tankies,” the people who still think the Soviet Union was justified in sending tanks into Hungary in 1956. Thus I began the process of radically revising what I thought about the modern left.

Then I stopped myself. Because that would be crazy.

As polls routinely show us, in any sufficiently large group of people, you will find some small faction who believes basically any nutty thing you can come up with. David Icke, for example, is apparently able to make a decent living telling people that the world is ruled by blood-drinking lizard-human hybrids, one of whom was apparently none other than … Bob Hope. Yet the world has managed to largely contentedly ignore him for years, despite the sizable crowds this high-test twaddle apparently draws.

That’s hardly to say that insane beliefs are never worrisome — Hitler’s race theories were objectively stupid as well as incomprehensibly evil, yet they took over a country and almost a continent. But while we should care what crazy beliefs are out there, we should never assume that some fringe thesis is on the verge of consuming society.

That can be hard to remember with modern media hijacking the sort of natural filter most people use to assess social problems. For example, in the debate over “free ranging” American kids, one of the great mysteries is how Americans became convinced that children were under constant threat of being abducted by strangers, even as crime went down. One of the most compelling theories is simply that, while abductions haven’t risen, awareness of them has.

Before the 1980s, you would see a local abduction reported in your newspaper perhaps every few years. But then came cable news, and suddenly you knew about all of the abductions. Because human brains are poor processors of large statistics, no one thought, “Oh, the rate is the same, but I’m getting more information.” They thought, “Eek! Lock up the children before someone steals them!”

Something similar happens to people on social media, particularly on Twitter. People can be sent into deep emotional funks by a few hundred strangers deluging them with abuse, precisely because our natural referents for this sort of behavior are personal and local, not statistical and global; as the numbers mount, it doesn’t feel like a tiny fraction of the world’s nasty people attacking a random target, but more like every person you’ve ever known, shouting at you in unison.

The good news is that the brain can eventually adjust; after nearly 20 years on the Web, my general reaction to strangers lobbing verbal grenades at me is “Oh, dear, so many people who clearly lack adequate meaning in their lives.” The bad news is that until habitation sets in, the Social Media Reality Distortion Field can confuse people into actually behaving as if the mob is significant.

Even large corporations, used to dealing with people in bulk, seem to be swayed by this illusion. It’s been rather startling to see how effective online mobs are at hounding workers out of jobs, or bullying corporations into punishing causes they don’t like, given that it takes less than a minute to compose an outraged tweet and perhaps 10 to forget that the whole thing even happened. Legislators know this, which is why they rank their constituent communications by how much effort they take, paying more attention to a letter or an in-person visit than to an online petition that took you a few seconds to sign.

But often, corporations seem to react to the numbers, without necessarily asking what fraction of that number is truly engaged. And it’s easy to understand how they might make such a mistake: On Twitter, we see endless outrage, while apathy is invisible; we’re given a massive numerator but never the denominator.

That is, we see a large number of people getting upset about something, their screams taking over our Twitter feed. But we don’t have a counter showing us that all those angry folks still represent 0.007% of Twitter’s user base, and an even smaller fraction of the world’s population. Nor, of course, are we told how many of them actually care, and how many are simply going along with their boss or their social circle.

That’s not to say that we should simply ignore social media. It’s genuine news when our tweeter in chief says something, even something incoherent. It’s certainly news when these platforms are used to coordinate real-word activity, such as the Arab Spring. And Twitter can also be useful in raising our estimates of groups we think are very tiny.

Just as I have now revised my guess at the number of hardcore Soviet apologists in the world, the 2016 campaign forced me to make a distressing reassessment of the number who hold warm feelings for Hitler. Yet I also reminded myself that when the user base is hundreds of millions, thousands of users saying the unspeakable is still closer to a rounding error than a vast social movement.

Of course, we should still keep an eye on that numerator, however small, simply because our target number of those people should be zero. But if we lose sight of the denominator, we’ll get a hopelessly distorted picture of how big a threat these people actually represent.