For lots of reasons:
A rifle requires line of sight. Not so with a drone.
A rifle will leave a ballistic finger print, and a gun that will need to be quickly disposed of.
A rifle will leave a loud sound that can be heard for blocks.
Secret Service are very suspicious of vans with their door cracked a few inches. Cameras are everywhere these days.
A remote control model plane can be sent from 15 or 20 miles away using video.
The payload of a drone is much better than a bullet or two.
With night vision, a drone can be sent at night in almost total invisibility, especially if painted black.
A barrage of radio control planes (25 or more) would be unstoppable.
Yes, this is a new screenplay called DRONE THE WHITE HOUSE, due out in theaters 2016.
I agree with all of this, except for the range estimate. Common radio control technology has a good enough range to be considered "beyond sight" and I've found that true with my RC hobbies. But if you don't have line of sight, I'd expect it to be less. Even a mile away is pushing it I think unless you spend huge money on some really fancy tech.
But anyway, the drone threat seems like a pretty serious one to me. It creates a completely new and unique threat with no clear solution. I have an idea though to solve the problem, and this will sound silly at first, but I am guessing its only a matter of time.
Fully automated intercept drones are the answer in combination with signal jamming and things like that.
You have a high performance quad rotor unit that is networked to a local radar system which specializes in identifying small objects within a set perimeter. Once the threat is detected, the drone takes of by itself, intercepts and engages with a semi auto shotgun loaded with bird shot or another disabling device.
I actually think it would work. Bird shot is less lethal for overshooting, but very effective at disabling small craft like that at close range (at least I'd think it would be). It needs to be automated and self operating. People don't have the skills and reaction time necessary to engage something that small and fast. We need help to be effective.
Now this alternative option will sound really silly, but I also think it
may work. Intercept eagles or other large, powerful, predatory birds that can be raised to identify and attack certain types of RC craft, in the same way dogs are trained to attack people.