Not that hard to do. A bunch of cans of gasoline, laundry detergent, and blocking the exits during sunday mass, and you could kill hundreds. Dynamite, and a bunch of ball bearings can do the same trick. Someone trained in how to use a sword can get to 9 also, see China where a group killed 28 and injured 113. Hell a wako driving a car on Santa Monica can kill that many and just gets you probation.
This is like the pit bull argument. Guns are bad, pit bulls are bad. While other dog breeds and other methods are used all the time. Yet the trigger word is guns.