I grew up on a myth: that the Jewish Revolt against Rome was virtuous and heroic; a fight for freedom led by saintly men. As an adult, however, I learned the truth: The Great Revolt wasn’t just an act of heroic anti-imperialist defiance, but an extremist folly that was, first and foremost, a civil war.

??It all started when the Zealots, a small extremist messianic group, seized power in Jerusalem. The populace, rabbis and priests distrusted them, but the Zealots took advantage of an opportunity: the outburst of public rage that followed Florus, the Roman procurator, arresting Jewish leaders and confiscating money from the Temple. The Zealots fought the Roman garrison in the city, though their main objective wasn’t the Romans, but the Jews. Now having a small army at their disposal, they displaced the moderate Jewish leadership and launched, against their counsel, a full-blown – and foolhardy – rebellion against the Roman Empire.

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The 'Trophies from Jerusalem' relief on the Arch of Titus in Rome.

As is always the case, extremists proved utterly inept at governing or waging war. The Zealots obtained only one victory against the Romans and then were methodically crushed in Galilee. In Jerusalem, the more moderate forces advocated for compromise. John of Gischala, the Zealot leader, left the battlefield (like most extremists, he was a coward) and returned to Jerusalem, not to fight the Romans, but to cement his power over his fellow Jews. The Sicarii, so called for their mastery of a short knife called Sica in Hebrew, used their skill to terrorize the moderates and quell dissent. That hunt for so-called traitors was an excellent excuse to consolidate power and eliminate opponents. Eventually, the people revolted against the Zealots, but it was too late. John, who’d had time to consolidate power, prevailed through sheer brutality. This self-described nationalist leader had no qualms about inviting a foreign army, the Idumeans, to help him suppress the rebellion. Eventually, John killed the Temple priests, dumped their bodies onto the streets for his Zealots to trample over, and then threw them to the dogs. Twelve thousand Jews were killed when the victorious extremists rampaged through the streets of the Holy City.

But as is always the case with fanatics, sooner or later another one tries to outdo them in fanaticism. In this case, John was challenged by another nationalist warlord, Simon bar Giora. Josephus tells us that, “He was a greater terror to the people than the Roman themselves.” A third group of zealots, complaining that neither John nor Simon was nationalistic enough, also broke off. A multitude of warlords were caught, “in perpetual slaughter.”

As the city descended into chaos and civil war, the Romans closed in and laid siege.

Inside the city walls, the situation resembled hell on Earth. Thousands of refugees crowded the city, which now had over half a million starving inhabitants. The dead were left to rot in the scorching summer sun and the stench was unbearable. Outside the city, Titus crucified five hundred Jews a day; inside, the Zealots poured Jewish blood like water. There was, in the words of Simon Sebag Montefiori, “intransigent fanaticism, whimsical sadism, and searing hunger.” Corpses were dissected for gold coins and, as hunger progressed, for seeds and crumbs. While dogs and jackals feasted on human flesh, the trapped Jews ate cow dung, leather girdles, shoes, and old hay. Josephus, an eyewitness to those horrible days, claims that, “No any other age bred a generation more fruitful in wickedness than this was, since the beginning on the world.”

The end of the story is known. As was predictable, the Romans took the city in an orgy of violence and pillage. The Temple, one of the wonders of the world, became a ruin and rivers of blood ran through the venerable esplanades. The damage that the “wicked generation,” in its fanaticism, inflicted on the Jewish People lasted for 2,000 years.

All because of extremism.

Judaism itself would have perished if Yeohanan ben Zakai, a moderate rabbi, hadn’t managed to escape the Zealots and negotiate with the Romans the reestablishment of the Sanhedrin in the city of Yavneh.

You may wonder why I chose to be so graphic in the description of the siege of Jerusalem. Believe me when I say that I’ve spared you the goriest details. I do it because it’s important to realize that the dangers of extremism aren’t theoretical or abstract. This is not some academic debate about the independence of the attorney general or ideal checks and balances in a democracy, but a matter of life or death for each and everyone of us.

The rabbis of the Talmud tried to inoculate us against the dangers of extremism. Writing in the aftermath of the tragedy, they described the Zealots with contempt and disgust. They called them Biryonim, meaning boorish, wild or ruffians. They condemned these Biryonim for their aggression, their unwillingness to compromise to save the survivors of besieged Jerusalem, and their blind militarism against the rabbis’ opinion to seek peace.

As they lay dying, the Jerusalemites of the year 70 might have wondered, “How did we get here? How could this happen?”

Throughout human history, true extremists were always a minority. They take power because several categories of enablers open the doors for them. All through history, those enablers look the same. There’s the selfish: “Yes, X is an extremist, but he’ll lower my taxes,” or “I know X is bad, but I need him to so that I can retain my power. There’s the arrogant: “Yes, X is extreme, but with my hands on the steering wheel, he can be controlled. There’s the sympathetic: ”Yes, X is extreme, but he has a point, doesn’t he?” There’s the corrupt: “Yes, X is extreme, but the system is broken and with him in charge we can take what we want.” And there are the “everybody does it,” enablers and the “it’s cool to be contrarian and ’own the libs,‘” types. Needless to say, the extremist ends up betraying all of them.

What’s so depressing about extremism is the resilience of the concept. Extremism has never worked. Not once. There’s not a single extremism that didn’t lead to tragedy. Many countries take generations to recover from extremist governments (see: Japan or Germany), and some, like my native Argentina, never do. And extremists suck at war. They’re terrible at combat because their victories come against those who don’t shoot back, like political dissidents and journalists (see: Russia). And they’re even worse at running the country’s economy because no economy can run without rule of law and judicial guarantees of property rights. (see: Venezuela). And yet, like a remitting and relapsing illness, in every generation people succumb to the bizarre allure of the extreme.

Seeing the tragedy that extremism caused, the Talmud disavowed zealots and zealotry, and created a culture of rationalism and open debate that instilled a democratic and freedom-loving attitude among Jews. The Jewish historical experience – in which we suffered in our own flesh the horrors of extremism – also should have vaccinated us against that illness.

But despite what Robert F. Kennedy Jr. may say, we aren’t genetically immune. We carry the recessive gene of extremism. Make no mistake, there’s no ideological difference between John of Gischala and [National Security Minister] Itamar Ben-Gvir. If Simon bar Giora had lived in the 21st century, he would feel at home in the Kahanist party. There’s no difference between the Sicarii of yore and the extremists that rampage through [the West Bank village of] Hawara today. And while some rightfully point to examples of extremism in other sectors of society, this is not a “both sides” situation, because although everybody is bound to the duty of moderation, Judaism teaches us that those in government always carry more responsibility and set the tone.

On Tisha B’Av, we commemorate the tragedies that extremism brought upon us. Or rather, the tragedy that we brought upon ourselves by tolerating and normalizing extremism: the destruction of our homeland and two millennia of exile and suffering.

Because most Jews today never lived in a time without a Jewish state, they can’t conceive of not having one. Because most Americans have lived all their lives in a democracy, they have no notion of how easy it is for a society to fall into extremism and tyranny. And yet, I can guarantee you that in 65 BCE, no Jew could conceive of the destruction of the Temple, a million Jews dead, or thousands sold into slavery and sent into exile. The “can’t happen here, can’t happen now” argument hasn’t worked very well for Jews throughout our history.

It’s maybe a warning from above that as Tisha B’Av approaches, Israel is locked in a battle between the better and worse angels of its nature, between extremism and moderation, between dialogue and discord, between cohesion and dissolution. It’s a battle that affects us all – and if Tisha B’Av serves for anything, is to teach that it’s one that we can’t afford to lose.

Andrés Spokoiny is president and CEO of Jewish Funders Network.