According to British home office estimates, there are 1,000 disaffected young Muslim men in Britain alone.
These young men are a potential recruiting ground for al-Qaeda or al-Qaeda- inspired terrorist organisations.
British leaders have been rightly careful to distinguish between mainstream, law-abiding Muslims and the actions of an unrepresentative minority.
It is impossible, however, to discount the fact that some of these young men will encounter people within their own communities who are only too willing to encourage and exploit their disaffection.
Until relatively recently, religion was underestimated as a factor in both war and terrorism. In Religion, Culture and International Conflict (edited by Michael Cromartie) Bruce Hoffman of the Rand Corporation analyses the relationship between religion and terror. In 1980, there were some 64 identified terrorist groups, of which just two were religious. By 1995, there were 56 terrorist groups, of which 26 were religious.
Hoffman observes that as the nature of terrorism has become more religious, it has also become more random and lethal. The predictable response from some commentators is that since religion seems to contribute to the forces of obscurantism and darkness, it demonstrates why religion should be relegated to history.
It is just this kind of attitude which makes religiously-inspired terrorism so hard to combat. It is necessary to know the enemy in order to have any hope of overcoming him.
Perhaps more importantly, if there is any hope for lasting peace, at some stage people have to enter into dialogue. Such dialogue is impossible without insight into what motivates the other. Few Irish people could have failed to have been reminded of the dark days of the IRA bombing campaigns when they saw Londoners once again emerging into daylight, dazed and uncomprehending as to why anyone would want to kill them. Not that there is an equivalence between the IRA and al-Qaeda. While religion may have played a role in the conflict in Northern Ireland, it was never invoked as a justification.
The IRA had a clearly defined agenda, and was ruthless enough to realise that taking bombs to Britain would bring the British government to negotiations far faster than any amount of bombs in the North.
On its worst days, it generally issued a warning that allowed some chance that loss of life would be minimised. The campaign was still murderous, though, and at one time, negotiations with the IRA were as incomprehensible as any form of negotiation with al-Qaeda seems today.
Yet those negotiations with the IRA became a reality, and no matter how stalled the peace process appears, it has taken on an inexorable logic, which must eventually end in the triumph of peaceful means, no matter how long it takes.
Perhaps negotiation with al-Qaeda is impossible, not least because we do not even know if al-Qaeda exists, or whether what we have instead is a loose network of people inspired by the example of Osama bin Laden.
What we do know, though, is that there is massive sympathy for bin Laden in parts of the Muslim world. If we are to minimise the likelihood of recruiting people who are willing to die for his cause, we must understand the world of Islam.
The signs are not propitious across Europe. The Netherlands is still reeling from the death of the film-maker Theo Van Gogh, and Somali-born Dutch MP Ayaan Hirsi Ali's life is under threat because of her disparaging comments about Islam. Not that she deserves death threats for her views, but her suggestion to Muslim women that they abandon their faith if they wish to be free, is hardly helpful. The essence of dialogue is that even where there is fundamental disagreement, that there is an attempt to put aside prejudice in order to understand.
We are very far from that understanding in the West, and there is little appetite for it to begin. We conflate "Arab" with "Islamic", yet the most populous Muslim country is Indonesia.
We conflate the most extreme distortions of Islam with mainstream Muslim belief. We are also guilty of a belief in the innate superiority of secular Western thinking, which means that we are unable to understand when a religious movement finds our culture both decadent and selfishly individualistic.
For true dialogue to take place, however, we cannot ignore the dark side of any religion, including Islam.
Every religion has an ideal form, which motivates its adherents. Sadly, the ideal form of any religion is rarely to be found in the real world.
The message of Jesus is one of peace, yet look at the wars and abominations that have been carried out in his name.
However, it would be a distortion to say that Christianity is always a force for violence, because history is full of examples, from St Francis to Martin Luther King, of Christians who made heroic sacrifices for peace. The Islamic ideal may be peace-loving, but is that visible in how Islam is lived?
You cannot enter into dialogue with either a distortion or an ideal, but only with the way in which faith inspires real people to act.
By 2050, demographers predict that one in every four people will be Muslim. That alone should give us an impetus to understand the various Islamic cultures. It should also allow us to put the hard questions. Where exactly does Islam, in its many forms, stand on issues like democracy and equality?
We also need to be prepared for hard questions in our turn, such as why religion is so often sidelined and marginalised in Western societies, not to mention questions about the greed on which our culture seems to be built.
Bertie Ahern said this week that a structured dialogue between church and State is to begin in Ireland.
Presumably part of that dialogue will be with our Muslim neighbours. It should be emulated elsewhere in the EU.
From France, with its refusal to allow the hijab in public schools, to Germany where a substantial Turkish minority has never been encouraged to integrate, such a dialogue is overdue.
The philosopher and mathematician Alfred North Whitehead said that the decisive moment when man progressed from barbarity to civilisation was when man moved from reliance on the use of force to reliance on the use of persuasion. You cannot persuade someone you do not know.