Years earlier, Monis had been on ASIO's terrorist watch list, although he was removed from it in 2008. He had been charged numerous times for sexual assault; he had also been jailed. His rhetoric became more extreme and he declared his support for Islamic State. Two days before the Sydney siege, an anonymous caller to the anti-terrorism hotline warned authorities about Monis' state of mind. ASIO investigated, but decided he wasn't a threat.

The report of one of the later inquiries recommended that, in response to the siege, states and territories extend their so-called "extraordinary temporary powers" laws. These laws, among other things, allow police to detain suspects for a limited number of days without charge, to protect public safety. This "preventive detention" requires only that police believe a threat exists.

The report's recommendation was unusual; after all, police and intelligence agencies had had the opportunity to use these powers to detain Monis. They didn't, but nor should we have expected them to. Some said a wildcard like Monis should have been under closer observation and stopped. Yet others, such as former White House counterterrorism adviser Richard Clarke, said the siege wasn't terrorism at all, describing Monis as "someone who was committing suicide by police, as a lot of people with mental problems do".

We cannot prevent every "lone wolf" attacker like Monis, no matter how draconian our laws become. Nor are we likely to suffer many such attacks. Our intelligence agencies are far better prepared and funded than they have ever been to counter terrorism. Nonetheless, preventive detention laws have only been used twice in Australia since they were introduced a decade ago. For all the arguments for tougher security legislation, this simple fact demonstrates that the risk of specific, preventable attacks – as perceived by law-enforcement authorities themselves – remains low.

Indeed, the Commonwealth's former independent reviewer of security legislation, Bret Walker, SC, said preventive detention should be scrapped, as the laws are "much more trouble than they are worth" and even "worse than useless". As he put it: "Should we, as a society, give consideration to ... [preventive] detention orders against violent husbands, drunken or adolescent drivers, or careless foremen? Surely not. Have we properly articulated the reasons why counterterrorism should produce an opposite response?"

In 2013, a separate review commissioned by all Australian governments, led by Anthony Whealy, QC, recommended states and territories ditch preventive detention. It pointed out ASIO already had questioning and detention powers that served the same purpose.

Nonetheless, every government ignored the advice. This week, the ACT became the last jurisdiction to extend the powers. Justice Minister and Greens MLA Shane Rattenbury was the only member of the ACT government to oppose the change. Attorney-General Simon Corbell acknowledged the laws infringed on nine legislated ACT human rights, notably freedom of movement and liberty, and the right to a fair trial.

In short, these barely used powers, which expert advisers say are unnecessary, violate the central principles of Western liberal democracy. This doesn't mean the powers are useless. But their existence comes at a price; they sap our commitment to freedom. It's a shame our governments are so fearful of being seen as weak on terrorism that they barely even discuss this price before saying "yes" to more, broader powers.