My DC doesn't know, but doesn't believe so, rather that they were silly, naive, and got swept into something that they shouldn't.
Then at the very least you might ask the question "so what is a degree in History at the University of Warwick teaching in terms of graduate skills of critical thinking?"
It's been noted in the past that one interesting thing about terrorists who have degrees is that they are almost always STEM, and even the Unabomber (Maths) is something of an outlier. The interesting thing in this case and the related cases at Exeter and St Andrews is that with one exception it's all non-STEM: law at Exeter, History at Warwick, English (and other things, it's slightly hard to tell, but it doesn't look like STEM) at St Andrews. The exception is the ringleader at St Andrews being Maths, but that case is slightly different to the other two: the motive seems more personal and there isn't (not that it makes it any better) the same air of wide-ranging misanthropy.
If you were doing a factor analysis, I'd put money on the dominating characteristics being "Privately educated" and "A Level History". Which is a PhD in itself.
These are all courses in which men are in a minority, so it's not that they are being somehow egged on by the overwhelmingly male environment they find themselves in. Most of them are conventionally good looking men, well-dressed, looking confidently into the camera, and they are in hugely female-dominated courses in hugely female-dominated universities (Warwick is slightly STEM-ier than Exeter and St Andrews, but they're none of them Herriot Watt, are they?) It's not like a rogues' gallery of Incels, fresh from basements, which is what makes them more terrifying.
Hideous people, and their psychopathy would be very interesting if anyone had the stomach to study it.