What that suggests, too, is that we should be smarter about how we deal with those who return, and those at risk of going. The understandable response so far has been a policing and criminal one, but criminalisation is not the whole answer. Where there is evidence of participation in atrocities, returnees can be prosecuted – one of the ways that social media works in civilisation’s favour in this story. The vast majority of returnees to date, however, have not been charged. Fewer than half have even been arrested. Often there isn’t enough evidence to convict them of anything, or anything serious enough to send them to prison for long. Sending people to prison is about the best way you can devise of ensuring that they remain radicalised, and perhaps infect other prisoners around them.