France, of course, has no Second Amendment. French gun laws are pretty effective at keeping weapons out of the hands of law-abiding French citizens. Terrorists not so much.
And the point is not that terrorists shooting up a theater with fully-automatic AK-47s could be outgunned and stopped by a few concealed carriers armed with pocket .380s. The point is that having somebody–anybody–in the theater who can shoot back disrupts the terrorists’ plans, perhaps pins them down for awhile, and buys time for people to escape or help to arrive.
And finally, if you’re gonna die, it’s better to go down fighting than to be slaughtered like a sheep.