The title of this post refers to France, of course. I'm going to explain why it might be a good thing if the Islamists target France, which they are apparently threatening to do.
The French, and the rest of Old Europe (after 3/11 including Spain), are still locked in a pre-9/11 mindset of appeasement and viewing terrorism as a law enforcement problem (see Droopy for an American example). This mindset was in retrospect a disaster for the U.S., as we had opportunities to nip Al Qaeda in the bud but wimped out. The key point, however, is that it took a major terrorist attack on U.S. soil for us to take the problem seriously. If France were similarly attacked, it would force their hand. They would have to once and for all choose between appeasement and joining us in going after terrorists.
It's possible they would choose to continue in their EUroweeny ways. Even if this is the case, however, it would expose their policy as weak and ineffective and encourage others to join us. I think that the French people would view this as unacceptable, and bring in new leadership if they did not respond to an attack. The French government elites can spew and sputter about the cowboys in America, but if they were in our position they might be forced to take action because of popular opinion. The French currently see humbling the U.S. as more important than protecting their people; an attack might change this.