What worries me most about the riots is not the riots themselves; it is their disturbing similarity to the trigger events of the previous two World Wars, along with all the political and economic dry powder lying around. All the reading from various blogs I've done and I've only seen hints of this point here and here. The continental Europeans have a history of denying problems and taking the easy way out until things are absolutely out of hand, and then suddenly solving the problem by turning it over to a fascist dictator. Who, upon discovering that his policies aren't really fixing the problems after all, comes up with the brilliant idea of trying to externalize the problem.
Traditionally, this is by attempting military conquest. The military situation of today is of course radically different than fifty years ago and that's not really on the table in any reasonable time span, nor can I really see a France of any kind making a credible nuclear threat. But even though I can't name it, I'm sure they can think of a way to make a lot of people's lives unnecessarily miserable.
When you have eliminated the impossible outcomes, whatever remains, however improbable, must be the possible outcomes. There are only so many ways forward. A priori, "France becomes a fascist state" must be considered a very low probability outcome indeed. But as you start eliminating all the other outcomes that either aren't occuring ("police put down the riots swiftly and effectively") or almost certainly can't occur ("France learns the error of her ways and moves to more effectively integrate her immigrants, by among other things giving up much of the Socialist Dream"), how many probable outcomes are left? At the very least, every day that goes by that the riots get worse, the good outcomes recede farther and farther away, and I am left hoping against hope for "the riots die out on their own"... which if they were going to, they probably should have by now.
This is scary stuff; those low-probability outcomes are coming up on us faster than intuition can readily grasp.