WHEN three girls, aged 15, 16 and 17, left Bethnal Green and ran off to Syria, we didn't know how to react.

Were they vulnerable? Were they victims who had been groomed? Or were they clever, autonomous, high-achievers, who knew exactly what they were doing? Only the latter reaction, I believe, would have occurred had they been boys - and there have been cases of young men around such an age who have gone from America, Britain and Australia to fight for Isis. Boys would be talked of as radicalised. They would be assumed to know what they were doing. They wouldn't even be called boys - just young men. Grooming and victimhood would barely get a mention.

So it's odd that it does here. This reaction over the past few days is, I suspect, as much about our anxieties around teenage girls as it is about Islamic radicalisation. And it doesn't help us get to the bottom of the real question of why they left, and why others like them do. One of the problems of talking about these girls as victims or vulnerable, is that we eliminate discussion about what it is that motivates them or causes them to reject British culture. We blame, instead, the groomer, some sinister older other. We neglect the bigger question of why the ideas resonate, why both young men and women are lured by what seems to most of us a horrifying nihilistic death cult.

Indeed we can end up denying the fact that these girls might have very actively thought through what they did. The sociologist Frank Furedi, writing in Spiked Online, believes this is the case. He notes that while the Bethnal Green girls may have been impressionable, "to cast them in the role of vulnerable passive victims of ruthless groomers is to overlook the obvious point that they are active young people who, for better or worse, took the initiative to make a radical choice. There is now evidence that, far from being groomed, one of the three girls was actively searching for contacts online."

Across our culture we are struggling with the question of how much autonomy young people should be allowed, and to what degree they should be protected from their mistakes and manipulation by others. Here in Scotland, we considered it right to allow 16-year-olds to vote. In the UK, more than 10 per cent of army recruits are 16-year-olds. More than one in four are under 18 - though at least we do not allow them to fight until they are 18.

Many of the girls who go out to Syria are around the ages mentioned here, some only a little younger. They were recruited by other young women like themselves. To what extent do we credit them with their own thoughts and self-determination?

Like Furedi, I'm uncomfortable with a position that treats their behaviour as purely the product of naivety and the vulnerability of youth. Most research suggests that women who join terrorist organisations tend broadly to be driven by the same motivations as men. Research by Kamaldeep Bhui, Professor of Cultural Psychiatry and Epidemiology at Queen Mary University of London, found that British jihadis were likely to be educated and come from wealthy families, but feel bored and socially isolated. He found that girls were as likely to radicalise as boys. Many of these young people, male or female, had a "youthful naïveté". In other words, perhaps 15-year-old girls are not so very much more vulnerable than some 20-year-old boys - or any more susceptible to online grooming.

So, why do they do it? When, not long ago, I interviewed the Muslim academic Mona Siddiqui, we discussed why intelligent young British women might be going to Syria to join the jihad. Her belief was that such radicalisations said "a lot about their own family backgrounds or contexts, rather than foreign politics". She also suggested that the desire to be involved in struggle may be at the heart of it. "For some it could be that it seems thrilling," she said. "Life is so comfortable now that it's lost any struggle."

If this is the case, then simply saying to these girls that it's going to be tough or horrifying may not put them off. It's possible they already know it, that it's part of the attraction. I find it hard to believe that those three Bethnal Green girls had not been aware of the many shocking stories of how women have been treated by Isis. Perhaps they dismissed them as propaganda. Perhaps their recruiters reassured them they were untrue. But they must have had some lingering suspicion that such horrors are out there - and yet gone anyway. And that is all the more frightening - and also more difficult to understand than the idea they were victims, groomed and lied to.