The "big dogs" who weren't themselves dying for the cause could have other selfish motivations: desire to advance in a particular political structure by impressing people with their effectiveness or by scaring away their opposition, desire to do something that will go down in history and not be forgotten, sheer hatred, sheer ego, psychosis, or any combination of these or other reasons. They don't necessarily think they're doing the "right" thing, just what will get them personal gain or prove that they're the best.

Keeping score of moral achievement is tough. Keeping score of dollars earned, votes tallied, or people killed, those are quantifiable achievements. Or look at it another way, if Osama bin Laden was just a multi-millionaire construction magnate, who would have heard of him? It's not having the money, it's doing something high-profile with it. And it doesn't get much more high-profile than this. Plus (at least in the past) whenever he hits the US he gets the automatic adulation of a lot of people who are inclined to dislike the US for one reason or another. Adulation is also heady stuff.

Or think about teenagers in gangs. They will do incredibly awful things to other people to prove their way into the gang, to prove that they're as tough or tougher than anyone else in the group. They know they're not doing the right thing, but being "in" and being respected proving they're not weak (and being afraid of what their "friends" would do to them if they showed weakness) becomes more important to them than what's right or wrong.