Terrorism will only cease to be a threat when extremist ideology is marginalised.

'A terror attack is intended to send a message that civilians are not safe in public places.' Photo: Reuters

The horrific bombing of the Boston Marathon, killing three and injuring 282, demonstrated that the ''age'' of Islamist terrorism against Western civilian targets - heralded by the September 11, 2001 attacks - is not over. The terrorist threat has neither been neutralised nor relegated to the past.

The first step to combating terrorism is to accurately identify the motivations behind attacks. Therefore, in the immediate aftermath of Boston, when little was known, blind speculation about the perpetrators or motives was indeed counterproductive.

However, this changed once evidence mounted that Tamerlan and Dzhokhar Tsarnaev were the perpetrators, and that lead plotter Tamerlan, at least, was a disciple of radical Islamism.

What is now counterproductive is to refuse to acknowledge that the attack was part of a wider reality of terror motivated by the spread of transnational, violent and radical Islamist ideology.

Today, thanks largely to the internet, violent, radical Islamism can be propagated not only in Islamic countries, but also in Western societies - even without any direct recruitment by operatives from organised groups such as al-Qaeda (although a face-to-face ''radicaliser'' is usually involved).

The fact that Tamerlan Tsarnaev apparently left a social media trail that included a link to provocative videos by Australian cleric Sheikh Feiz Mohammad only underlines the global reach of the radical Islamist movement. It also demonstrates that Australia continues to play an important role in countering this global problem, despite (or perhaps, conversely, especially because of) the success, to date, of Australian authorities in preventing anything similar happening domestically.

Meanwhile, some are now arguing that terrorism should be accepted as a normal hazard of modern life, like traffic accidents. Others draw false comparisons between terrorist acts and the rampages of mentally ill gunmen tragically endemic in the US. These sentiments fail to acknowledge the unique characteristics and goals of terrorism. Terror attacks are perpetrated by immoral ideologues, not the mentally ill. This is true whether the terrorist is acting alone or as an operative in an organised network.

As the instigator for terrorism, radical Islamism is not the only global actor, but it is a major player, and to deny this is to deny reality.

A terror attack is intended to send a message that civilians are not safe in public places. The fear that is created by terrorism is leveraged by the indiscriminate nature of the attacks. More than an atrocity, it is an assault on the social contract underpinning society. Moreover, successful terrorist attacks tend to encourage others and touch off a savage game of one-upmanship in a drive to capture global media attention.

Escalating terror can lead to significant economic and social costs to society, as security concerns disrupt normal life. And escalation could lead to truly horrific outcomes involving WMDs.

Terrorism thus involves costs far beyond the immediate damage caused. For instance, terrorism has required airport security measures impacting air travel convenience and costs. But the alternative would be much worse - frequent hijackings or downing of airliners that could decimate international commerce.

Those who insist that responding to terrorism can only breed more terror as a counter-reaction ignore the evidence of history.

While it is certainly true that, for example, Osama bin Laden's demise did not mean the end of al-Qaeda, it is beyond dispute that al-Qaeda is far weaker today than a decade ago. There is no evidence to support the notion that easing off on measures against Islamist jihadists will lead terrorists to reciprocate. Rather, past hints of such a relaxation has been viewed by extremists as a ''victory'' to be used as a recruitment tool.

Opposing terrorism - particularly radical Islamist terrorism which we witnessed in Boston - remains a moral duty and an overwhelming national interest, but it requires long-term vigilance.

It involves not ignoring state-sponsored terrorism - there is no more egregious case of this today than that of Iran - and taking every necessary step to isolate and pressure such states. It also means preventing the development of new terror safe havens - in Mali or Yemen or Syria, for instance.

Here in Australia, it requires careful processing of immigrants, overseas visitors and, yes, asylum seekers, to prevent the exploitation of a compassionate system by those who would plot or recruit for terror attacks.

Vigilance also means significantly assisting mainstream Muslims in their responsibility to not only disassociate themselves and criticise extremism, but actually expunge it from in their communities and to develop a ''counter-narrative''.

At the end of the day, Muslims are best placed to lead effort to combat intellectually the ideas of the Islamist extremists who claim to act in the name of ''true Islam'', and thus finally unravel this threat.

For just as communism ceased to be a threat only when that ideology lost its appeal, it is only when radical Islamist ideology is marginalised and discredited globally that the conflict with Islamist extremist terrorism will subside.