Of late, the British media has been full of reports about the dangers posed by citizens who have gone to Syria to fight the Bashar al-Assad regime.

The apprehension is that at least some of these radicalised Muslims will return, trained and battle-hardened, to launch terrorist attacks within Britain. These fears are shared by many European countries with large Muslim populations that have contributed fighters to the Syrian civil war.

Currently, there are an estimated 2,000 citizens of European countries reported to be fighting in Syria. Recently, one of them, Abu Suleiman al-Britani, drove a truck laden with explosives into Haleb prison in Aleppo. This suicide attack, carried out by the Al Nusra Front, an Al Qaeda affiliate, enabled some 300 prisoners to escape.

Most of these foreign volunteers fly to Turkey and cross the border into Syria. Here they are guided to various resistance groups, but mostly, they tend to join extremist units. Two Muslim clerics have been identified as preachers who are using the Internet to urge young people to join the jihad.

Last January, 16 young Britons were arrested as they returned from Syria, while seven are awaiting trial. They stand accused under Section 5 of the Terrorism Act, 2006, which makes it a crime to fight abroad with a “political, ideological, religious or racial motive”. Those found guilty can be sentenced to life in prison.

But as George Monbiot reminds us in a recent article in the Guardian , thousands of foreign volunteers flocked to Spain to join the International Brigades fighting General Franco’s fascist power grab against an elected socialist government in 1937.

Among them was George Orwell who, according to Monbiot, would have been arrested and jailed under the Terrorist Act. Even back in 1937, the Foreign Enlistment Act of 1870 was reactivated to deter British volunteers; however, nobody was prosecuted under this law.

Another famous writer who went to Spain during the civil war was Ernest Hemingway, and For Whom the Bell Tolls is based on his experiences during that bloody conflict.

My father was studying for his doctorate in Sanskrit drama at Sorbonne University in those exciting days, and told me about the ferment among leftist circles in Paris. Several of his friends crossed the border into Spain to join the International Brigades.

So is the era of idealism over? Or is it that some struggles have a greater moral claim on our conscience than others? Is it more politically correct to honour those fighting for social justice based on an egalitarian worldview, while punishing those carrying out a jihad to restore the Caliphate and impose Sharia law?

We can point to the terrorist attacks carried out by Islamist extremists to justify our rejection of the whole movement. But the truth is that jihadis don’t have a monopoly on violence against non-combatants: the 19th century Anarchists shook Europe with their campaign of indiscriminate violence.

They, too, had utopian goals, believing it was essential to topple the state before their vision of the perfect society could be created. And American forces have never shirked from inflicting civilian casualties in their wars from Vietnam to Afghanistan.

Ultimately, terrorism is a weapon of the weak. Suicide bombers don their explosive vests because they have no tanks or jet fighters to confront the state. Asymmetrical warfare has been a recurring theme in military history as the only option available to weak forces when facing organised and well-equipped armies.

The key ingredient that gives the smaller side a chance of success is motivation based on idealism. For young British Muslims to leave the comfort of their homes and risk their lives in a distant land they know little about needs a high level of idealism.

But the fears of European governments about the potential of these jihadis to carry out terrorist attacks in their own countries are not misplaced. Long before the Syrian civil war began, many terrorist attacks have been carried out or planned by young Muslims born and brought up in the West. So there are reasonable grounds to suspect that at least some of these volunteers will represent a threat to security.

Recently, there were newspaper reports to suggest that the Al Nusra Front has put together a unit with the express purpose of recruiting Muslim volunteers from Western countries. Apparently, they are to be indoctrinated and trained to carry out operations on their return. And as citizens of the European Union, they would be free to travel across the Western world without needing visas.

Seldom has a conflict been so widely reported by participants on Facebook and other social media. The allure of adventure and comradeship forged under fire makes for a powerful recruitment tool.

Photographs of young combatants posing with machine guns, together with their occasionally boastful accounts of derring-do, make their friends back home envious, filling them with the desire to fly to Turkey en route to Syria.

Faced with a threat whose potency is amplified in the minds of security analysts, it is probable that governments in the West will take no chances, and simply lock up anybody suspected of having visited Syria recently.

This is unlike Pakistan from where volunteers have been fighting under the banner of jihad virtually since the beginning of the conflict. Our authorities have shut their eyes to the dangers posed by these fighters. But as we discovered after the Soviets left Afghanistan, blowback is a long and painful process that endures long after the conflict has ended.