This article by Robert Ferris does a decent job of highlighting some of the issues currently with off the shelf drones and the threat they represent. The real problem though is you can see how little thought has gone into deal with drones. Ideas like compelling manufacturers to put Geofencing firmware on the drones makes little sense since many hobbyists will simple change/hack the firmware. Certainly malicious actors will. Furthermore many drones do not rely on GPS alone to fly and/or GPS can be fallible unintentionally making a drone go of course. Worse still bad actors can “meacon” or manipulate sensors and or GPS on drones to make them go where they want. For these reasons more active defense capabilities are needed.
Low cost drones are rapidly becoming more feature rich and capable. Most of these do not represent much of a security risk, other than video, because even though they are feature rich and low cost the physics of battery life and weight vs lift ratios limit their air time, payload, and thus ability to do more than be very short term ISR platforms. That being said soon platforms as capable as the the very popular DJI Phantom will be reaching this price point. At that point drones that can become a threat will become ubiquitous.