Osama bin Laden talks about "defeating the Great Satan for the glory of Allah and Mohammed (pbuh)" for the same reason George Walker Bush talked about "spreading Freedom and Democracy": because it resonates with his intended audience, convinces them that he has similar thought-processes to them and is representative of their interests, or at the very least their team, not because he actually believed that that was what he was doing.

There is a problem with arguments of the form, "The leader of that group clearly doesn't 'really' believe his own rhetoric he's just saying that because it resonates with his followers." This implies that their followers actually believe that stuff, otherwise there would be no point in the leaders' saying it. But you've just admitted that there exist people who really believe that stuff, why is it so absurd for the leader to be one of those people?

I certainly agree that I should not model their minds as being identical to mine, but given that I don't want to kill people, I'm already doing that at least to some degree.

You're still self-anchoring. You observe that they want to kill people, so you try to imagine under what conditions you would be willing to kill people.

That said, I think that you are being overly simplistic in your model of these people.

Well, near as I can tell, your model boils down to "they secretly have to same world-view as I do, and the difference in their rhetoric is because it resonates with their audience".

For the record I should probably mention my model:

They observe that the Islamic world isn't as powerful as it was in its glory days. Furthermore, the West and the United States in particular is influencing their culture in ways they don't like. Solving this problem requires a model of how the world works. Well, the model they turn to is one based on Islam.

There is certainly more that could be added to this model, e.g., a discussion of how feuds work in clan-based societies for starters.