In 415 BC, Athens was at war. Its maritime empire had stumbled into a fight with the land power Sparta, and the asymmetry in the way both cities projected power ensured that the war dragged on for years. In the middle of this, Alcibiades, a brilliant, handsome, doomed aristocrat, brought a motion before the Athenian voters: Athens should invade and conquer the island of Sicily. No one knew very much about Sicily, or what sort of defence the Sicilians would mount. But they were confident that the Athenian reputation would precede them, and off the fleet sailed.
The Sicilian expedition was a disaster. The biggest city on the island, Syracuse, turned out to be well fortified and not particularly cowed. The Athenians who were sent were, quite predictably, defeated, and those who were not killed were enslaved. As one reads the story of Athens gratuitously opening a second front in what was a very hot war, one wonders how they could have been so stupid. It's tempting to dismiss this as some primitive story from the ancient world. But if Alcibiades were alive today he'd be in advertising, where his ability to manufacture demand would fit in. Slick advertisers recognize that if you can get people to listen, you can make them desperately want something they'd never heard of ten minutes ago. Athens was particularly vulnerable to this sort of thing because democracy was direct: people could vote on anything immediately after hearing a motion proposed.
Nowadays, we can experience for ourselves the joys of direct democracy on the internet. Moral fashion driven by social media often has this effect: a new moral imperative arises that no one had heard of last year. Consider the dictate that everything must be more diverse. Even if we look past the short term results, the really troubling thing is that the strategic questions remain unanswered. Growing 'diversity' in France has seen a spike in antisemitism leading to a spike in Jewish flight. And like the Sicilian expedition, this result is entirely predictable. Antisemitism is widespread in the Middle East, of course large scale immigration will also import this attitude. The trouble is that no one specified whether diversity entails a diversity of opinions on whether Jews ought to feel at home in France. The problem is that, as with the Sicilian expedition, we are in too much of a hurry to get to terra incognita, to stop and pick up a map.
A friend commented on an earlier post about the ways in which mass movements are like schooling fishes, asking what defence there is against these things. He's right that schooling is itself a defensive behaviour, and for that reason alone there are psychological pressures to join in. Animals who could selectively avoid herding would be evolutionary cheats – and arguably evolution selects for an ethical baseline, perhaps squeezing such cheats out. Maybe that is the explanation for what I find most remarkable, which is that the phenomenon I am describing, which we could call it political correctness, or manufactured demand, or "the Sicilian expedition trap", does not already have a name.
Fortunately, you don't have to resist the herd, you can just avoid it. Jaron Lanier's recent "Ten Arguments for Deleting Your Social Media Accounts Right Now" (the listicle title demonstrates another malign internet influence) is only the most recent plea for less tweeting and more reflection.
An older answer is the liberal arts themselves. Want to know what to do about the problems you find in Thucydides? Start by reading Thucydides.