Illustration: Andrew Dyson That's why there's a catharsis in stripping citizenship from these people. It's a secular act of excommunication. And, just like its religious counterpart, it makes us feel better about those still in the fold. We're purifying ourselves of disbelievers. But this implicitly requires us to view terrorism in one of two ways: either as war, or as unconventional politics. The war analogy, of course, has dominated our discourse on terrorism since the September 11 attacks, and explains why it is that the only other way for a dual national to lose an Australian citizenship acquired at birth is to serve in the armed forces of a country fighting ours. But hereabouts we run into problems. First, that if the post-9/11 era has taught us anything, it is that treating terrorism as war has been a ghastly failure. It has only compounded the disaster and amplified the problem to the extent we now consider a terrorist attack on home soil more likely than at any other time in our history. But secondly – and more intriguingly – this approach is increasingly at odds with the way governments and security organisations are talking about terrorism. This is the era of "radicalisation"; of lone-wolves and kids succumbing to radical propaganda. Islamic State, as it confronts us in Australia, is not a conventional army or even a structured terrorist organisation, but a movement to which people recruit themselves. That's why the Prime Minister spends so much time talking about the role of the internet. It's why we talk about young Muslims being "groomed" by recruiters in a similar way to the victims of paedophiles. We're beginning to recognise that we can't simply bomb terrorism out of existence. The task now is to persuade people not to be seduced. No military can do that. That is a task of politics. The trouble, though, is that we take the logic of terrorism as politics only so far before we abandon it. Take the other major recent development: Australians who've gone to Syria only to discover that beneath Islamic State's utopian promise is a gruesome lie. Now they're trying to get out and come home. And as more Australians inevitably make the same discovery, we'll see a lot more of this.

This might just be the best news we've had in a year. We've been sweating on precisely this kind of crack in the edifice of IS propaganda. The truth is that we can brand IS as "death cult" all we like. We can condemn it on some kind of relentless loop if it satisfies us but, in practical terms, none of it means a thing when it comes from the mainstream. Radical politics expects mainstream rejection – indeed it requires that for its own legitimacy. When we tell ourselves how evil IS is, we need to be clear: this is a performance for our own benefit, not to persuade people who might otherwise be charmed. The one thing radical politics cannot withstand is when its own true believers reveal its hypocrisy. The Caliph may have no clothes, but it's his subjects who must call it out. And yet it is precisely at this juncture that we refuse to take advantage. Asked about the possible return of such people, the government eagerly reiterates: we don't want them back, but if we must receive them, we have no interest in anything other than punishing them. That impulse is easy to understand: after all, the crime is clear. But is the impulse strategic? Are these people of more use to us stuck in Syria than they would be telling other Australians about the horrors of IS with vastly more credibility than anyone else? Is the aim to punish them, or stem further recruitment? Are we after vengeance, or some manner of victory? To be clear, I'm not advocating such crimes go unpunished. Even the lawyers of these people accept they'll be prosecuted. But it's telling that we can see nothing beyond this; that we so resolutely refuse even to acknowledge this potential gift because we're too busy reiterating our hatred for these people. Somehow, it was easier to accept the idea of Soviet spies defecting to the West in the Cold War than it is for us to imagine someone might have joined ISIL naively, and has discovered their error. Are these people of more use to us stuck in Syria than they would be telling other Australians about the horrors of ISIL with vastly more credibility than anyone else?

Maybe that's because they rejected us first. Maybe it's an extension of the catharsis we feel when we extinguish someone's citizenship. But here's the danger: by rejecting anything that doesn't begin and end with condemnation – as if by reflex – we're surrendering the politics of terrorism in precisely the way ISIL so effectively isn't. Waleed Aly is a Fairfax Media columnist and winner of the 2014 Walkley award for best columnist. He also lectures in politics at Monash University.