The means by which France, or any other nation, could defeat the terrorists are obvious: to compel the majority of French Muslims to turn against the terrorists, the French authorities would have to make them fear the French state more than they fear the terrorists.I'm certain civil libertarians believe Spengler's cure is worse than the disease. And they may be correct.
That is a nasty business involving large numbers of deportations, revocation of French citizenship, and other threats that inevitably would affect many individuals with no direct connection to terrorism. In the short term it would lead to more radicalization. The whole project of integration as an antidote to radicalism would go down the drain. The effort would be costly, but ultimately it would succeed: most French Muslims simply want to stay in France and earn a living.
The dilemma is that Muslims are estimated to be 10% of the French population. As a start, the French need to reassert governmental authority in the "no-go" areas where most Muslims reside, in itself a major undertaking.
France also needs to remember the basic rule that applies when discovering one has dug oneself into a hole: stop digging. France needs to turn off the immigration tap, and stop importing trouble. Other nations, including the U.S., should do the same.