Here in Delhi I've been attending some sessions of the 2015 India Today Conclave, a wide ranging conference on all manner of subjects relating to Indian politics and society, and India's place in the world.

There was a fascinating panel discussion yesterday on the threat of ISIS, featuring two men who survived long periods of captivity by extremist groups in in the Middle East. If you watch the early parts of the video, you will see a convener who is perhaps a little too eager for the two men to recount the lurid details of their experience; they respond with extraordinary dignity and wisdom.

Also on the panel was Princeton University Professor of Near Eastern Studies Bernard Haykel, who made an argument about the threat of so-called returning foreign fighters that I have never heard in Australia. The discussion about these fighters is dominated by the fear that they will be a threat to Australia when they return home, but Haykel makes the blunt and arresting argument that those who go to Syria and Iraq to fight for ISIS don't want to come back. They burn their bridges with their home country when they leave, and even burn their passports. They are leaving to fight and to die, not to return as trained terrorists.

But Haykel goes further: he says it is a mistake to even prevent those who want to fight for ISIS from leaving, because when their ambitions are frustrated, they become a 'lone wolf' threat at home.

I sat down with Professor Haykel in a busy hotel lobby after his panel session to discuss his argument: