There was a lot of mess already with the current immigration crisis. Now add that attack, and like you said, it's a powder keg, except I'm afraid that this shooting may have just lit the fuse. People will be connecting those two issues. They already are, judging from things that start popping up on my Facebook feed.
I fear the overreaction coming, of both citizens and governments. I fear the Europe will split, or start a war with someone, or draconian security measures will be introduced by the government. Charlie Hebdo was symbolic. This was a real terror strike. I just hope that sanity prevails and we won't amplify the damage further.
> I fear the overreaction coming, of both citizens and governments.
This is pretty much the standard official and media reaction to these kind of events. You're supposed to fear the "backlash" more than the terrorism. Yes, dear French people, this was bad, but the real catastrophe would be voting for Le Pen or ending Mid-East and African immigration.
That's what the OP probably meant. If you think about it, don't you think it is a somewhat unnatural reaction to being under attack, to always end up fearing those who didn't initiate the attack?