There are a number of Youtube videos of people flying hobby drones well above 10,000 feet. Above 10,000, several safety measures go out of effect - airline passengers can remove their seat belts, airliners can exceed 250 knots, etc - so a hobby drone at 10,001 feet is much more dangerous than a drone at 9,999. Above 18,000, all flights must be conducted under IFR and pilots are no longer required to see and avoid - so they stop looking out the window and get busy with other tasks. So a hobby drone at 18,001 feet is yet more dangerous still, as well as being a whole new level of illegal.
You can bet your bottom dollar that hobby drone operators know none of this.
The FAA, for very good common-sense safety reasons, wants like hell to put a stop to this. However, Congress legislated away the FAA's power to actually regulate or provide standards for hobby drones. The FAA can't say "don't fly them above 10,000 feet" because they are now prohibited by the FAA Modernization and Reform Act of 2012 from *any* rulemaking regarding model aircraft. And according to the Act, the model aircraft can be *up to 55 pounds* - and it seems like FAA concepts like "controlled airspace" don't apply. The only requirement is that if you are going to fly within 5 miles of an airport, the operator has to provide prior notice - *not ask permission* - from the airport's air traffic control.
During the period 1958-2012, the FAA was solely responsible for aviation safety and airspace regulation, and maintained a profoundly excellent safety record. From 2012, there are now two agencies responsible for air safety - the FAA for manned aircraft, and vaguely-defined "community-based set of safety guidelines" for recreational drones in the same airspace. Common sense says that this can't, and won't, work - so basically, Congress has decided that we will wait until a drone takes down an airliner, then over-react and probably outlaw all hobby drones everywhere. And probably blame the FAA.
This is what passes for policy-making in the US today. It's really very sad.