I can understand it, I just don't buy it personally. But that's not the point. They realise, quite correctly, that 'The West' will never be defeated through military force. So instead they adopt a far more clever strategy: play upon most Westerners most innate fears, and they will serve up to you what you desire.
And it's a strategy that has worked well and continues to work well in a secular climate.
See, when you're not afraid of death. When you start to consider it as something that's at the least not unpleasant and at the best glorious, then it's hard to control you by terror.
Think about it, peeps.
What do you fear most? Leaving your children behind whilst they are young. Losing your children whilst they are young. Most of us would do anything - give up anything - to keep them, and ourselves, 'safe'.
To the fanatic, however, there is no fear of such things, b/c to the fanatic, God will take care of these matters.