Like others, I have been shocked by the reluctance of many of Israel’s critics to feel, let alone express, disgust at the atrocities perpetrated by Hamas on October 7. This determination to look away calls for an explanation — a reckoning, you might say.

The victims of Hamas were not collateral damage during a military operation. The mission’s purpose was to inflict organised sadistic savagery not just on helpless non-combatants but on terrified mothers and children, the elderly and infirmed. With hundreds still held hostage, this unspeakable cruelty is ongoing. If such depravity fails to shock the conscience, what would it take?

Yet many young Americans rallied in support of Hamas, either looking past this evil, defending it or in some cases actually celebrating it. Their position appears to be that in the conflict between Israel and Hamas, Israel is the aggressor, the oppressor, the coloniser; the people of Gaza are the victims, the oppressed and the colonised. From this they deduce that whatever Hamas does, it cannot be in the wrong.

This self-willed moral blindness masquerading as principle underlines the dangers of fundamentalist thinking in which political theory overrules basic human decency. But fundamentalism does not ineluctably lead to fanaticism, and they are not one and the same. The distinction matters because fundamentalism should be questioned and challenged, whereas fanatical violence must be suppressed.

In the political realm, fundamentalist thinking makes history surrender to all-encompassing theories. Classical Marxism is the paradigm example. Postmodernism has yielded modern fundamentalisms with roots in that world view and dominates parts of US academia. But the appetite for theories to guide action, grounded in one or two core insights, is not confined to colleges or the cultural Left. The world according to intersectionality and offshoots such as decolonisation theory are undeniably fundamentalist. But hardcore neoliberalism has been called, not unfairly, market fundamentalism. Conspiracy theories tend towards fundamentalism. “Drain the swamp” can be understood as a reductive theory of what is really going on.

Some such theories are stupid, but others are deep and illuminating. An open-minded reader can learn a lot from Marx while detesting the systems built in his name. Many contain kernels of truth and few are wholly wrong. But by definition all of them are reductive and simplistic — and to that extent intellectually flawed.

The educated liberal mind is sceptical and recognises theories, however insightful, as tentative and refutable. It’s critical race theory, not critical race revelation. Universities have woefully failed their students by suppressing intellectual competition among rival schools of thought, installing just one family of theories on power, oppression and justice as a secular religion. Embraced by faculty and administrators alike, it comes complete with ritualised declarations of faith. The more preposterous these are — “colourblindness is racism”, “speech is violence” — the more they are prized as affirming commitment. In many colleges today, dissent on such questions is all but forbidden. Heretics are not hired, and those already on the payroll keep quiet.

This monoculture is terrible for educating students and forming citizens. It makes democracy harder to sustain, because it inclines believers against debate and compromise. It leads them to think that the task of democracy is to deliver the one true just society — and to neglect democracy’s most important purpose, which is to mediate disagreement, so that people can live together peacefully and productively. Colleges should insist on intellectual pluralism and model a civil society in which compromise is possible, where pragmatism and rival fundamentalisms engage in debate and in which fanaticism is roundly rejected.

While fanaticism can spring from fundamentalism, it does not have to. Toxic on a whole other level, it might start with a Marxist account of justice, power and oppression but then adds bigotry, unyielding refusal to compromise and lust for violence. The fanatic’s watchword is “by any means necessary”, and he means it.

The young Americans who say they “stand with Gaza” are surely wrong to excuse or divert their minds from what Hamas did, but of course they are not all dangerous fanatics. Some just want the violence to stop. No doubt, others marched in solidarity with Palestine because this seemed right and their friends were going. Many may be sincerely against the right of Israel to exist as a sovereign state. These true-believer anti-Zionists are in thrall to a bad theory that casts Israel solely as a wicked coloniser, but I’m assuming not many of even these think it is good to kill children so long as they are Jews.

We have now seen that this latter proposition encapsulates exactly what Hamas thinks. By any means necessary. Its members are not just fundamentalists; they stand revealed as murderous fanatics. They should be universally despised and condemned.

The failure to see this, the reluctance to admit it — to say nothing of declarations defending or praising the atrocities — show something is broken in higher education. Decent people, whatever their intellectual attachments, critics and supporters of Israel alike, should be united in this. Maybe the backlash against the universities’ response will force America’s educators to stop and think. If a case such as this won’t do it, what will?

• Clive Crook is a Bloomberg Opinion columnist and member of the editorial board covering economics. Previously, he was deputy editor of The Economist and chief Washington commentator for the Financial Times