How about shooting the knives out of his hands? Maybe just wing him in the finger slightly? Hitting him in the knee might keep him from walking, hitting him in the hand and the worst is no longer being able to pick his nose with that finger.
1) We can blame this kind of claptrap on the anti-gun culture. Because people don't have much contact or experience with guns, they think that all it takes is a little practice to become a gunpoweder William Tell. They understand neither what people nor what pistols are capable of.
2) People, because they have such weird notions about firearms, think that LEO's clearly have the time to develop almost super-human skills of marksmanship. They don't realize that MOST LEO's are never in a situation where shooting is required and that many of us aren't compensated for time we spend practicing at the range -- while we are expected to know a whole huge bunch of other stuff.
Ignorance of firearms and ignorance of the basics of Law Enforcement (I've been guilty of both) lead to a lot of very silly thinking.