I'm not sure I agree with geofencing, but it's also true that drone operators appear to be, by and large, acting like complete jerks and someone needs to get the message across somehow.
A jerk owns a drone? Better pick on the non-jerks!
A bad guy used encryption? ...
The message shows be sent by levying fines, mandating community work and putting restrictions from operating drones for X years for anyone caught being a jerk.