My wife,who isn't especially interested in political science, asks the best questions. This morning, watching the news, it was "why are they doing this?" I tried running through the complexities and models, and quickly lost her. Then I realized I could make sense of it as the intersection of two sets of rules.
Rule (1) The first rule of Islam: There is no God but Allah and Mohammed is his Prophet. This rule made sense when unifying countless polytheist groups under a single banner, and it's still useful for prostletizing today. It makes it clear who's "in" and who's "out". It states there is only one true path, and it implies that anyone not on that true path is stupid, or evil, or both. It is not a matter of "religious tolerance". Islam is _right_ in a way nothing else can approach, and by insulting the Prophet you have insulted God.
This rule in and of itself is not sufficient to motivate violence, and there are other religions with similar rules. There are still a lot of Christian churches where rule one is that you are "born again" or forever damned.
So that brings us to rule (2).
Rule (2) The first rule of tribal society: If you have been wronged you must take revenge. Again, it's a practical rule for operating as a close-knit group in a hostile environment. By itself, it doesn't identify what is and is not a wrong.
Now combine rules (1) and (2). By publishing these cartoons God has been wronged and we must avenge.
This would explain, by the way, why we don't see such a violent reaction among Muslims outside of the Arab world (or immigrants with a strong connection to those cultures). Both rules have to come into play to create the effect.
I'd be the first to admit this is simplistic. But to the extent that it is true, there are two long-term solutions:
1) End Islam, or
2) End Tribalism
I doubt option (1) is possible (as well as being immoral). It seems the long-term policy, therefore, has to be option (2). Democratize, modernize, globalize, whatever you want to call it, the point is to get enraged people to go to the courts and the ballot box, not to the street.
Addendum (2.17.06): My wife read the above and commented that I didn't really get to the root of her question. She was especially interested in where are that rage comes from. She's right; there's much more going on than the sort of 'reasoned anger' suggested by the post above. And, as she observed, much of that rage is related to a general sense of being harmed by the imperialists. This, in turn, is encouraged by regimes (and others) who want to deflect criticism of themselves by pointing to a scapegoat.
Sometimes I wonder if the best thing we (the 'West') could do would be to pull out and take away the scapegoat. It wouldn't work. As long as we exist, we can used as an excuse for indigenous failures. Israel, of course, can't pull out, nor should it have to stand alone. And in an interdependent world, especially with an oil economy, what happens there will inevitably have a major impact here.
(Damn. I wish there were easy answers.)