As far as I can see, there can be no debunking. However, you should also bear in mind that a lesser jihad is _supposed_ to be a purely defensive fight.
It is also specifically supposed to stop attacks on non-combatants.
However, Osama bin Laden has used his own interpretation of the Qu'ran .. which is pretty typical of fundamentalists, IMHO.
Most moderate Moslims appear to be consigning his fatwah to the rubbish bin
Unfortunately, less moderate Moslems, particulary those who have an axe to grind against what they see as 'the great satan' may take his call as justification for their atrocities :-(
Regards Sadim