This feels to me like a just world fallacy, or perhaps choosing the most convenient world. Yes, if the barbarians are completely stupid, they are probably not so much of a danger these days. If they are completely anti-science, we probably have better guns.

Now imagine somewhat smarter barbarians, who by themselves are unable to do sophisticated science, but have no problem kidnapping a few scientists and telling them to produce a lot of weapons for them, otherwise their families will be burned at stake. (Even if their religion prevents them from doing science, they may compartmentalize and believe it is okay to use the devil's tools against the devil himself.) Suddenly, the barbarians have good guns, too.

Maybe the reason why the West hasn't been conquered by Muslim fundamentalists yet is that Muslims don't have an equivalent of Genghis Khan. Someone who would have the courage to conquer the nearest territory, kill horribly everyone who opposed them, let live those who didn't (and make this fact publicly known), take some men and weapons from the conquered territory and use them to attack the next territory immediately, et cetera, spreading like a wildfire. First attacking some smaller but civilized countries to get better weapons for attacking the next ones. With multiple leaders, so that dropping a bomb won't stop the war. (Maybe one Osama hiding in secret, giving commands to dozen wannabe Genghis Khans who don't mind getting to paradise too soon.)