What leads young European Muslims in the thousands to give up lives in France, Britain or Germany, enlist in the ranks of the movement calling itself the Islamic State, and dedicate themselves to the unlikely aim of establishing a caliphate backed by digital propaganda?

The honest answer is that we don’t know why a 20-something Briton with a degree in computer engineering or a young Frenchman from a Norman village reaches a psychological tipping point.

Zealotry of any kind subsumes the difficulty of individual choices into the exalted collective submission of dedication to a cause. Your mission is set. It is presented as a great one with great rewards. Goodbye, tough calls. Goodbye, loneliness.

Islamic State has been adept in exploiting the alienation felt by many young Muslims, from the “quartiers” of Paris to the back streets of Bradford. It offers to give meaning, whether in this life or the next, to meaningless lives.

The group has benefited from active support by online jihadi preachers and from tacit backing, or at least acquiescence, from imams in some mosques who are inclined, in the words of Prime Minister David Cameron of Britain, to “quietly condone.” It has manipulated anger over America’s wars in Iraq and Afghanistan, over Abu Ghraib and Guantánamo, over Shia ascendancy in the Middle East, over bleak existences on the margins of European society.

Still, the explanations fall short. Plenty of people experience great hardship or prejudice without opting to behead infidels and apostates, practice codified rape on teenage nonbelievers, and pursue the establishment of God’s rule on earth through his chosen caliph and in accordance with Shariah law.

Every effort of Western societies, particularly since 9/11, to curb the metastasizing jihadi ideology that threatens them has failed. Some of the organizations that grew out of that ideology have been hurt. But the ideas behind them, rooted in a violent rejection of modernity (but not all its tools, witness the Islamic State’s slick use of the Internet) and in an extreme, literalist interpretation of certain teachings of Sunni Islam, have proved of unquenchable appeal.

It’s a long way from Yorkshire to Raqqa in eastern Syria, yet some young British Muslims make the trip. Other recruits arrive from Saudi Arabia and Russia, Libya and Australia. The Islamic State has demonstrated very broad outreach. It is clearly tapping into something deep. Perhaps that something is at root a yearning to be released from the burden of freedom.

Western societies have been going ever further in freeing their citizens’ choices — in releasing them from ties of tradition or religion, in allowing people to marry whom they want and divorce as often as they want, have sex with whom they want, die when they want and generally do what they want. There are few, if any, moral boundaries left.

In this context, radical Islam offers salvation, or at least purpose, in the form of a life whose moral parameters are strictly set, whose daily habits are prescribed, whose satisfaction of everyday needs is assured and whose rejection of freedom is unequivocal. By taking away freedom, the Islamic State lifts a psychological weight on its young followers adrift on the margins of European society.

Mark Lilla, in an essay this year in The New York Review of Books on the French novelist Michel Houellebecq’s “Submission” (whose central character, a disaffected literature professor, ultimately chooses to convert to Islam) made this important point:

“The qualities that Houellebecq projects onto Islam are no different from those that the religious right ever since the French Revolution has attributed to premodern Christendom — strong families, moral education, social order, a sense of place, a meaningful death, and, above all, the will to persist as a culture. And he shows a real understanding of those — from the radical nativist on the far right to radical Islamists — who despise the present and dream of stepping back in history to recover what they imagine was lost.”

Lilla concluded that Houellebecq sees France in the grip of “a crisis that was set off two centuries ago when Europeans made a wager on history: that the more they extended human freedom, the happier they would be. For him, that wager has been lost. And so the continent is adrift and susceptible to a much older temptation, to submit to those claiming to speak for God.”

In Europe right now, those speaking most ardently for God tend to be Muslims. Some of them have spoken out bravely against the Islamic State. A majority see the movement as a betrayal of their religion. But the jihadi temptation to escape from freedom into all-answering zealotry is there and will not soon be curbed.

It is interesting that another foe of the West, President Vladimir Putin, attacks its culture from a similar standpoint: as irreligious, decadent and relativist, and intent on globalizing these “subversive” values, often under the cover of democracy promotion, freedom and human rights.

The great victory in 1989 was of freedom. But every triumph stirs a counterforce. The road to Raqqa is the road from freedom’s burden.