Crowded spaces it's a problem, I was more talking to notion of just plain shooting them rather than a use case. A rifle would be dang near impossible, but a scattered spray, you really only need to stop one prop and it's probably on the ground for a standard 4 prop deal. At least mine got real screwy when a blade split mid flight.
Edit: It also could be noted that while a lot of pellets would miss, they would pose a lot less risk that a rifled bullet coming back down. The weight of an individual shot pellet is a fraction of the weight of a bullet, so less momentum, plus the don't have a ballistic spin to maintain their speed that a rifle round does. Basically someone shooting a shot round in the air would come down with about as much force as a handful of gravel once the air resistance slows it a bit.