The 17 people detained in the counter-terrorism raids last week and this week in Australia account for fewer than half the total number under close ASIO monitoring, according to sources involved in the effort.

The courts ultimately will decide how many of them have broken the law. But already it's clear that the revival of the threat posed by the Islamist-terror complex will be upon us for years. The number of people under surveillance, and the fact that the coalition military operation against the barbarians in Iraq has yet to begin, should signal that this phenomenon has far to run.

In the meantime, half-truths, hyperventilation and hyperbole run amok. On one hand, fear-mongering magnifies a real threat. We know that one of the terrorist suspects was planning to snatch an unsuspecting member in Martin Place, behead him while filming and post it to YouTube, right?

Not according to the acting commissioner of the Australian Federal Police, Andrew Colvin. Asked about this on ABC TV, he replied: "Look, I think what we need to do is understand that the plot was about violence against members of the public. Now, how that was actually going to manifest itself, we're not 100 per cent sure."

So we don't actually know it at all. Media reporting got way ahead of the facts.

Colvin, remarkably, then went on to invite us to use our imaginations: "Beheadings, obviously, is something that we're concerned about, but we shouldn't narrow our thinking just to beheadings… You could think about shootings or knife attacks - a range of things. That's why we just - we don't want to narrow down our - the range of possibilities too much just at the moment."

Is this to be the new evidentiary standard of federal law enforcement? "You could think about…"? 

The prime minister properly assured us not to change our behaviour in response to the threat of terrorism, but then went on to give us a good old scare anyway: "It is a serious situation when all you need to carry out a terrorist attack is to have a knife, an iPhone and a victim."

If you weren't feeling apprehensive before listening to Tony Abbott, there's a much higher chance you were after listening to him.

It's not that he's incorrect, it's the fact that he's supposed to be the man ultimately responsible for national security, not insecurity. The terrorists trade on fear – that's why they're called terrorists. 

Abbott went on to say that the police raids on Thursday had been intended as "a show of strength, it needed to be a show of   strength, it needed to be a demonstration that we will respond with  strength to any threat to our way of life and to our national security."

And then immediately: "I do have to say, though, that the challenges that we face are more serious today than at any time in the past."

Is Abbott seeking to reassure or to alarm? Judged by his words, he is trying to do both. Give us a frisson of fear, but also offer the assurance that he is our protector. And by accentuating the danger, he emphasises  his position as protector. 

Is it true that the dangers are "more serious today than at any time in the past"? That's a big claim. More serious than when the Japanese Imperial Army subdued all of Asia and began its invasion of Australia with bombing runs on Darwin and midget submarines sinking shipping in Sydney Harbour?

More serious than the threat over the past decade when Australian courts have jailed 26 people for terrorism-related crimes, including Melbourne's Benbrika ring for plotting to attack an AFL grand final and to assassinate a prime minister?

Eugene Rogan, a professor of the modern history of the Middle East at Oxford, says that "there has been a massive overreaction" in the West to the terrorist threat from the barbarians of the so-called Islamic State.

"We do risk empowering those we most want to weaken by overreacting," he tells me. "Sixty Australians," who, according to the Australian government have joined the movement in Iraq and Syria, "is not a huge number, that's really very few" from a nation of 23 million.

Even the estimated 500 Britons who have joined, he says, is a figure that needs to be kept in perspective in a country of 64 million.

"We will make them stronger and more appealing and make it look like we're on the run."

Perspective is always the hardest thing to find when fear is afoot, memories run short and deadlines run even shorter. 

The federal government's 2010 counterterrorism white paper said that the terrorist threat had become a "persistent and permanent feature of Australia's security environment" and that an attack "could occur at any time".

So this is not a new phenomenon. And a statistical analysis of the relative risks of death by terror attack in Australia makes clear just how much success, luck or both that the country has enjoyed in recent decades.

A paper by John Mueller of Ohio State University and Mark Stewart of Newcastle University in 2010 demonstrated that the chance of being killed by a terrorist act in Australia from 1970 to 2007 was one in 33.3 million. The chance of death by traffic accident, by comparison, was one in 15,000.

And, on the other hand, we see a seductive argument for Australian inaction in the face of the new barbarians. The Greens tell us that we shouldn't contribute forces to the coalition to crush the barbarians because it will increase the risk of terrorist attack at home. And it's not just the Greens. An analyst at the ANU Strategic and Defence Studies Centre, John Blaxland, told the Financial Review: "If we move to take on IS directly…then it only escalates the terror risk to Australia."

This argument is wrong for two reasons. First, Australia is already firmly established as a target for Islamist terrorism. 

The alleged plotters who were rounded up in Sydney this week were first detected and put under surveillance by ASIO in May, George Brandis tells us. That was a month before IS's sudden capture of the Iraqi city of Mosul and the West's awakening to the need for action. 

Second, Australia's place as a target is enshrined in the fundamentalists' eschatology. According to Sidney Jones of the Jakarta-based Institute for Policy Analysis of Conflict, a line in an oft-cited jihadist hadith, or report of the Prophet's words, says: "You will fight the Romans and Allah will give you victory" in the great battle at the end of time. 

The Islamists interpret this to mean that the Romans are "represented today by the West, including America, Australia and Europe", according to Jones. This will remain fixed whether Australia contributes military forces to an international coalition or not.

The alternative to action is inaction. One of the key lessons of the past three years is that inaction in the face of chaos is to invite wider chaos. It was because the Syrian civil war was allowed to rage unchecked for three years that IS moved to Syria, fed on the mass death, grew strong and attacked this year in Iraq.

Inaction today would validate its success and invite wider chaos and more bloodshed. Barbarians are challenging civilisation. Australia should defend civilisation. It is in our deepest interests. We will be attacked whether we do or not.  

To confront aggressive barbarism with lethal force is necessary, but also insufficient. 

It's the generals who are saying so. The Pentagon itself, the military headquarters of the coalition, explains that it is the ideology of IS that needs to be destroyed and "that's not going to be defeated through military means alone," the Pentagon spokesman, Rear Admiral John Kirby, said this week. "It's going to take time and it's going to take good governance and responsive politics, both in Iraq and in Syria."

The former chief of the Australian army, Peter Leahy, now at Canberra University, concurs. The big lesson of the last decade, he says, is the limits of military force: "The big-ticket item is radical ideology. It has at its core the creation of a caliphate, the destruction of existing governments, and the installation of sharia law."

This is the heart of the matter. The barbarians' big claim to credibility is that they lay claim to represent Islam. They do not, but the appeal to a romantic idea of recovering a lost Islamic empire has power.

Australia can do better. Australia has to demonstrate that it is more welcoming of true Islam and more tolerant than IS. And it is. An important study released this week by Charles Sturt University's Centre for Islamic Studies and Civilisation showed how mosques in Australia are gradually integrating into Australian life. English is now the dominant language, the study found, and most mosques now cater to multi-ethnic congregations. Australia is a free country that welcomes freedom of worship and draws strength from diversity. We need to make that abundantly clear. It is, as Leahy says, the big ticket item in this contest.

IS, on the other hand, is the epitome of intolerance.

So far, the Abbott government is pursuing the right policies at home and abroad. This is good for Australia, and good for the Abbott government.

A prime minister neither liked nor trusted has a great opportunity to show that he can be respected. But he will need to resist the temptation to go the extra step, to go too far in dramatising a serious national problem and appear to be exploiting it.

Abbott came to power promising a grown-up government. In pursuing the deadly threats to civilised life, he has his big chance to deliver.

Peter Hartcher is the political editor.

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