Why do we insist on ignoring what stares us in the face? The suicidal fanatics who threaten to kill us in the name of their perverted brand of Islam are not refugees from Syria, or deranged zealots from the mountains of Pakistan: they are, with only very few exceptions, men and women who were born in our hospitals, educated in our schools and who grew up in our cities.
The men who carried out the attacks in London in 2005 were born and raised in Leeds, Bradford, and Huddersfield. The men alleged to have carried out the Paris attacks last week were born and raised in Belgium and France. The men who murdered Lee Rigby two years ago were both born in London to Christian parents from Nigeria.
Many of the attackers were already known to the police. Some had records as petty criminals. Others had clear links to identifiable terrorist groups. So as we still struggle to comprehend the crime that was committed in Paris last Friday night, perhaps we should start by examining what is going on under our noses.
That means asking difficult questions about why some young men growing up in Europe feel so alienated from the society in which they live that they want to destroy both it and themselves. In particular, it means thinking about the way our leaders use words like "we" and "they". The scholar Ian Buruma put it admirably: "We know that a dangerous minority of young people are attracted by reasons to die. What is needed badly is a superior reason to live."
It might also be useful to acknowledge the past. In the words of the Harvard professor Stephen Walt: "Decades of misguided U.S. and European policies have left many people in the Arab and Islamic world deeply angry at and resentful toward the West. Those policies include the West's cozy coddling of various Arab dictators, its blind support for Israel's brutal policies toward the Palestinians, and its own willingness to wage air campaigns, employ sanctions, or invade Middle Eastern countries whenever it thinks doing so suits its short-term interest."
But this is at best a partial explanation, because it fails to address the very obvious fact that the jihadi phenomenon is also a real threat to people and places far beyond the shores of Europe and the US. The simply stated goal of the killers is to force everyone, wherever they live, to bow to their will.
Ask the people of Bangladesh, Egypt, Kenya, Lebanon, Libya, Malaysia, Mali, Nigeria, Pakistan (have we really forgotten the attack in Peshawar less than a year ago, when 130 schoolchildren were massacred?), Russia, Tunisia, Turkey and Yemen, all of whom have suffered grievously at the hands of jihadi zealots. And ask the people of Raqqa in Syria what it is like to live under the rule of these brutal fanatics.
So what can we do to confront the danger? Here is my 10-point plan:
1. Improve the way our intelligence services process the information that is already available to them. (I am not convinced that they need extra powers, although see 4. below.) They seem to be pretty good at identifying potential threats; they are not so good at keeping a close eye on them. Five of the Paris suspects are thought to have fought for IS in Syria before returning to Europe, so why were they still able to plan and carry out their attacks?
If that means increasing the intelligence services' budgets so that they can take on more staff, then let's increase their budgets. The more data they collect, the harder it will be to sift what matters from what doesn't. If it were up to me, I would abandon both the British and the French nuclear weapons programmes and concentrate resources on defence against today's threats, not those of 50 years ago.
2. Have a long, frank talk to the security authorities in Belgium, which is emerging as the weakest link in Europe's anti-terrorism campaign. According to the Brussels-based analyst Bilal Benyaich: "Brussels is a black hole in Europe's anti-radicalisation policy. It is easier for people with bad intentions -- be they criminal, mafia, or terrorist -- to live life under the radar here than in any other major European city."
3. Keep a much closer eye on what is going on in Europe's jails. Prisons and the internet are the two key drivers in what is known as "radicalisation", the process by which vulnerable, confused young men can be turned into suicidal killers.
4. Look again at the way encrypted social media and instant messaging technology can be exploited by terrorist groups. I am deeply reluctant to allow the State any further access to our private communications, but we need to be clear-headed: if fanatics are planning massacres undetected because the authorities can't decrypt their communications, we need to deal with that.
5. Similarly, the EU should suspend the Schengen open-borders regime that enabled the Paris killers to cross back and forth between France and Belgium without anyone noticing. It will be a huge nuisance to millions of travellers, as well as damaging to EU trade, but I suspect the families of those who were killed in Paris will regard it as a price worth paying if it helps to prevent future attacks.
6. The UK should join any EU or NATO military action aimed at weakening the IS in Syria and Iraq. That means principally cutting off its supply lines and access to revenues from illicit oil sales (currently running at an estimated $1.5 million per day), something that should have been done months ago.
7. Put pressure on Turkey to stop attacking Kurdish units who are fighting IS on the ground and tighten up its border controls to stop the flow of personnel and supplies to IS units in Syria. Remind President Erdogan that France is a fellow-NATO member and deserves full support from Ankara.
8. Make it crystal clear to the rulers and clerics of Saudi Arabia and the Gulf states that they need to dissociate themselves in both word and deed from the groups responsible for bringing so much misery to so many people. The growth of IS is in part a result of the proxy war for regional supremacy between Saudi Arabia and Iran, and it has profound security implications for the rest of the world.
9. Intensify diplomatic efforts together with Russia and Iran to forge a ceasefire in Syria leading to a transition to a post-Assad future. The downing of the Russian plane in Egypt last month means the prospects for diplomatic progress are now better than for a very long time.
10. Resolve not to fall into the jihadis' trap. They want to create an unbridgeable rift between Muslims and non-Muslims, and between their brand of Islam and all others, including Shi'ism. We should do the opposite: build bridges, strengthen ties, create alliances.
The French journalist Nicolas Hénin, who spent 10 months as an IS hostage in Syria, described his captors as "street kids drunk on ideology and power". "Everything convinces them that they are on the right path and, specifically, that there is a kind of apocalyptic process under way that will lead to a confrontation between an army of Muslims from all over the world and others, the crusaders, the Romans. They see everything as moving us down that road."
He also wrote: "They will be heartened by every sign of overreaction, of division, of fear, of racism, of xenophobia ... Central to their world view is the belief that communities cannot live together with Muslims, and every day their antennae will be tuned towards finding supporting evidence."
Our goal, surely, Muslims and non-Muslims alike, must be to prove them wrong.