"Powell said it was right to make concessions to Sinn Féin. 'We certainly believed there was every chance that the IRA might go back to violence, just as they had with the Canary Wharf bomb [in 1996].'"
So, Powell is conceding that the government was always conscious that it was negotiating with a gun at its head. (This approach to negotiation is also fundamentally unfair to the peaceful parties that the government was dealing with). Now, just imagine how much more extreme the fear of al Qaeda returning to violence would be and you see the huge problem involved in talking to them.