Governments and anti-extremism organisations have understandably taken notice. They see the reach and influence of the medium and want to use it to curb extremism. The instinct is right. The execution is not. Take Pathways, the UK government-funded interactive game backed by Prevent and designed for use in schools. The game asks teenagers to guide a character named Charlie through online discussions about migration and British identity. Make the “wrong” choices – such as engaging with controversial posts or attending certain protests – and Charlie can be referred to Prevent or Channel, even given counselling for “ideological thoughts”. An on-screen...