It will remain forever a defining moment of the 21st century, a sentinel marker in an age when so much is quickly forgotten. This was the point at which the vulnerability of the United States of America - economically and militarily the most powerful nation in the world - was exposed. The opening sentence of the subsequent official commission of inquiry captures it precisely: "At 8.46 on the morning of September 11, 2001, the United States became a nation transformed." It was not nuclear weapons or an invading army, but a handful of ideologically warped terrorists engaged in a cowardly war, using means that even the most powerful nation in the world could not defend itself against. At 8.46am, a jetliner carrying thousands of litres of fuel slammed into one of the World Trade Centre twin towers in New York. Seventeen minutes later, a second plane flew into the second tower. Two more aircraft crashed that morning: one into thea Pentagon, another into a field after passengers overcame hijackers, armed with the knowledge that their nation was under attack. The huge twin towers burned then collapsed. Almost 3000 people died directly as a result of the attacks. Four years later, footage showing the first and second planes ploughing into the iconic glass-and-metal towers is no less chilling. These are events etched deep in the global consciousness of the information age.

There had been warnings of catastrophe, notably the bombing of the USS Cole in Yemen in 2000 and intelligence suggesting al Qaeda was preparing an attack of some sort in the US. Despite the prodigious intelligence-gathering of the US government community, no one had joined the do6ts. After the attacks came introspection. The 585-page report of the National Commission on Terrorist Attacks Upon the United States (better known as the 9/11 Commission) was released last year. It found that no one person or agency was to blame. It recommended refocusing national efforts on combating terrorism in a manner that centralised power and intelligence even further. The report drew praise from the Government but was widely criticised by others, one lcommentator concluding it "offers peace through exculpation, evasion, and entertainment and in doing so dangerously re-energises a national relish for fantasy".

The US engaged in a full-on war on terror that saw it engage and topple the government of Afghanistan, understood to have given succour to the leaders and foot soldiers of al-Qaeda, and then embarked upon a bloody and unfinished war in Iraq, named by US President George Bush as part of an "axis of evil". Australia and Britain have remained staunch allies in this war without borders or battlefields. Much of the rest of the international community, notably the European Union, is wary of the US approach. There have been some dividends. Libya appears to have relinquished its past as an enclave of terrorism, and there has been a push to reform and/ reinvigorate the United Nations.

Australians discovered they were not too remote from terrorism when bombers struck in the popular Indonesian resort island of Bali in October 2002. Of the 202 killed, 88 were Australians. The bombing attack on the Australian embassy in Jakarta one year ago underlined the fact that Australians must be considered targets of terrorist attack. Other attacks in Jakarta, Madrid and most recently in London have shown the struggle against this modern scourge is far from ended. There have been other debits. The climate of suspicion fostered since the September 11 attacks has, almost inevitablyc, led to an erosion of some freedoms.

So four years on from September 11, in a world that is fraught with dangers, what has the superpower learned? The answer to that conundrum may well lie much closer to home. When hurricane Katrina lashed the Gulf states a fortnight ago, America was exposed as vulnerable again. The death toll from this natural disaster will probably far exceed1 that of the September 11 attacks. But it is the Federal Government's response - or more precisely - its shambolic and hopelessly delayed response to Hurricane Katrina, that has caused Americans again to become introspective. Many Americans have been embarrassed and shocked by the depth of the economic and racial divide that has emerged from the chaos of New Orleans and the other affected communities. For a few crucial days in the immediate aftermath of the hurricane, far short of saving the world from tyranny, America looked as if it could not care for its own. The National Guard was diminished by the demands of the war in Iraq. Ironically, the Federal Emergency Management Authority - the body charged with the task of managing such crises - had been integrated into the terrorism-focused Department of Homeland Security. The loss of many disillusioned senior FEMA staff arguably left it ill-equipped to cope with the demands of the present crisis. Yesterday, the White House lost faith in the head of FEMA, Michael Brown, effectively sacking him.

Americans will determine whether the billions of dollars spent on the war against terrorism at the expense of other programs have been well spent. But on this day in particular, it is worth remembering how swiftly and irreversibly the world changed on that terrifying day in September 2001, and how America used its economic and political leadership to decisively respond to that event. Had it not, how much more vulnerable to terrorist attack would the world be today? That is almost impossible to answer.

The question is: do the changes to the Crimes Act and the associated anti-terrorism measures announced by the Prime Minister last week suggest a Government that is more alarmed than alert, or are they further evidence of political virtuosos who can spin the community's security concerns into political advantage? The answer is: it is a bit of both. But where alarm and spin combine to constrain personal freedoms without having much impact on the problem - terrorism - the community has reason to worry.

It is clear that the alienated radicals forming the splinter groups within international Islam are a threat to personal and national security, though the level of threat may well be overstated. Random acts of violence, whether remotely triggered explosions or suicide bombers, give people the jitters. Commuters bear the brunt of this unfocused fear, and governments have every reason to strengthen public safety measures on underground trains, the ferries, in bus and rail concourses and at airports. So closed circuit television, facial recognition software, a heightened security presence, improved passenger flow management and security drills are all reasonable, if expensive, responses that most people would support.

Greater intrusion into people's private affairs notwithstanding, the adjustments to the warrant system through which ASIO exercises its surveillance and monitoring powers are also reasonable. That is because that process demands reasonable grounds for the warrant and accountability on the part of the decisionmaker. And, what is of equal importance, the warrants have a termination date, thereby requiring review and re-issue if surveillance is to continue. In my experience, ASIO and successive attorneys-general have handled these matters with care and diligence. Although they might make us bristle at the inexorable march of "Big Brother", these are essentially administrative matters that the community can tolerate.

The proposal that it become an offence to incite violence within the Australian community or violence against our forces deployed overseas probably makes sense, even though the difficulty of proving incitement should not be underestimated. As we saw in the Spycatcher appeal in 1987, the courts take the view that "freedom of speech and disclosure of information (should) not be unnecessarily or unreasonably curtailed". Nonetheless, while a charge of "sedition" would be difficult to uphold, the provision would impose a serious constraint on those who advocate terrorist acts.

Of greater concern are the other proposals for legislative change that significantly increase the powers of government and the bureaucracy to constrain or curtail personal freedoms. Apart from the civil liberty and jurisprudence issues, we need to ask ourselves whether the threat is actually serious enough to warrant these changes, and whether they will be effective anyway.

Serious doubts attach to legislation permitting control orders, preventive detention, notice to produce and the extension of stop, question and search powers. Indeed, such powers, if targeted against the communities that might harbour terrorist sentiments, are more likely to exacerbate the problem than alleviate it.

What these measures fail to grasp is that terrorist cells cannot be eliminated using the traditional tools of legislation and law enforcement. They are not like criminal conspiracies that have structure, leaders, management and bureaucracy. Terrorist cells are ephemeral: they coalesce around specific terrorist operations, then mutate as other opportunities appear. They are opportunistic rather than targeted, which explains why terrorist events cannot be prevented absolutely. What governments, acting co-operatively, must do is to attack the causes and motives of terrorism by addressing the issues that alienate vulnerable communities and generate radicalism.

Australian governments have traditionally shied away from granting what are tantamount to royal commission powers to the police. The scope for abuse is too great. Yet the apparently unlimited scope of the notice to produce "information that will assist with the investigation of terrorism and other serious offences" has the potential to undermine both legal professional privilege and the protection of media sources. Similarly, the preventive detention proposal is far too open-ended, and lacks any sunset provisions that would remove it from the statute books when it is no longer needed. What is more alarming, however, is that these stern measures are unsupported by argument and evidence of threat. Nor is there any analysis of their likely effectiveness. And accountability is totally overlooked. It is here that one might suspect the victory of politics over reason.

Australia will not be more secure by becoming less free: our real defence is the rule of law, inclusiveness and prosperity.