.   "Likwise WMDs would be useless to any terrorist group,given that this would mean engaging the enemy head on"
Akenaton, remeber the 9/11 perpetraters' interest in crop spray aircraft? What do you think they had in mind?
It has become more difficult to hijack planes. Much easier to disperse anthrax, smallpox, radionucleides, nerve agent, ricin etc.