The savage terrorist murder in London of British soldier Lee Rigby, a Royal Fusilier, an Afghanistan war veteran, a husband and father, has once more shocked Western sensibilities.
The typical reaction is to describe the murderers as madmen.
In fact their action, and the chilling, surreal way one of the men explained it straight afterwards, is wholly evil but perfectly rational.
They see themselves as part of a historic religious and political war against the infidels, the West and all those whom they see as fighting Muslims anywhere. They are no more irrational than the equally murderous Islamist terrorists in Pakistan or right across North Africa.
In societies such as Britain, the US and Australia, with stable, affluent societies and superb, well-resourced security services, terrorist deaths have been kept to a minimum.
But before we trivialise the threat, we should recall that there have been 23 convictions for terrorist offences in Australia. Some of the plots revealed involved plans to attack Australia's research nuclear reactor and to inflict mass death at army barracks.
We also should remember that in one single terrorist attack in Bali, 88 Australians were killed.
The West is in danger of thinking that the war on terror is over and that those who hate our society have gone away, lost interest in us or given up the struggle.
Nothing could be further from the truth. The reaction to 9/11 brought an intense counter-terror effort in the West that has been remarkably successful, overall, in securing Western homelands. But things are starting to look quite a bit worse just now. This derives from the events in Syria and North Africa.
Of course, Syria is primarily a tragedy for the Syrian people.
The Syrian civil war is in its third year. Perhaps as many as 90,000 people have been killed.
About 1.5 million Syrians are refugees in nearby countries. Western intelligence agencies believe that as many as seven million Syrians eventually may flee their homeland.
This is a devastating humanitarian tragedy. It will also have implications for terrorism.
Syria is becoming a new ungoverned space that is attracting thousands of jihadists, as did Afghanistan a generation before. In Syria, these people will taste blood, learn terrorist skills and deeply internalise the most radical Islamist world view.
Many of them will then return to the Western nations of which they are citizens. Who knows what the results will be?
Australian security agencies believe that 200 Australians are in Syria participating in the civil war. Some are involved with Jabhat al-Nusra, the most effective fighting group in the Syrian opposition. Jabhat al-Nusra has publicly pledged its allegiance to al-Qa'ida.
Al-Qa'ida may be much weaker than it was as a central organisation - mainly because so many of its leaders have been killed by US drone strikes - but it remains a powerful brand, and organising principle, among jihadists.
The Western response to the Syrian crisis, which really means the US response to the Syrian crisis, has been feeble. But the US has no good options. Australia has done what it can by donating humanitarian aid to the Syrian opposition and to Syria's neighbours coping with the refugee flow. This is good work and the Gillard government has certainly done the right thing here. But broader allied policy, which again really means US policy, is ineffective.
So far, it has consisted essentially of masterful inactivity. But there is a cost and a danger to doing nothing, just as there is a cost and a danger to doing something.
A few weeks ago I interviewed senator John McCain, the magnificent voice of traditional US internationalism. McCain may or may not have made a good president but he is certainly a great man and his instincts that the US should help in every critical situation, and that US interests demand the deepest international involvement, represent all that is good in the American character.
McCain told me that the US should establish no-fly zones to prevent the forces loyal to Syrian President Bashar al-Assad from pounding opposition civilian populations. And it should provide both humanitarian aid and weapons to the opposition.
McCain told me that everything bad that people said would come about if the US did that - prolonged civil war, the radicalisation of the opposition, humanitarian crisis - has come about precisely because the US has done nothing beyond providing humanitarian aid.
McCain's thinking more generally is that the US could have shortened the conflict and empowered the more moderate elements of the Syrian opposition.
However, much as I admire McCain, I can also see the immensely powerful arguments against what he recommends.
For a start, the warring Alawite and Sunni populations live so close to each other that a no-fly zone would be very hard to make effective. It is not Syria's air force that is doing the lion's share of the killing.
Second, Syria is no Libya. It has advanced Russian air defences. It also has a huge stockpile of chemical weapons. It is supported with weapons from Russia, with weapons and personnel from Iran, and now with thousands of fighters from Lebanon's Hezbollah. Militarily confronting Russian equipment, Iran and Hezbollah in Syria may possibly be the right thing to do, but it is an enormous leap into the strategic dark.
Politically, it would be almost all downside for US President Barack Obama.
Dexter Filkins points out in a New Yorker essay that when a Black Hawk helicopter was downed and 18 Americans killed in Somalia, it was a terrible crisis for the Clinton administration. But doing nothing in the face of genocide in Rwanda, in which hundreds of thousands died, cost Bill Clinton almost nothing politically.
Then there is the question of what results US intervention would actually produce. As the war has gone on, the Syrian opposition increasingly has become dominated by the most extreme elements. But who is to say they would not have dominated anyway? What if the US enabled the dominance of a group that then slaughtered Alawites in their tens of thousands? Even arming the opposition is extremely fraught. What if the US gives surface-to-air missiles to the Syrian opposition, as it gave such missiles to the mujaheddin in Afghanistan, and these missiles are then used to shoot down Israeli or European passenger jets?
Yet as the war goes on, the dangers of inaction also grow. Syria's chemical weapons stockpile is so huge that as the rebels gain territory the chance that they will get their hands on this material increases.
The conflict shows once more the utter military impotence of Europe.
Recently Polish Foreign Minister Radoslaw Sikorski told me Europe was incapable militarily of handling the crises on its periphery. It could not even have done the very limited Libyan operation without US help. Militarily, as economically, the EU is a busted flush.
The failure of the Arab Spring almost everywhere, the rise of extremism across North Africa and the savagery of the Sunni-Shia split are all dynamics that assist the rise of the jihadists. The jihadists' hatred of the West is almost incidental in all this. But don't think for a moment that hatred has gone away.