There IS private airspace indoors (it is why drone races typically happen in warehouses or stadiums). Outdoors, there is no private airspace so much as there is

There IS private airspace indoors (it is why drone races typically happen in warehouses or stadiums). Outdoors, there is no private airspace so much as there is Class G airspace which is all airspace under 1200ft as long as you are out of range of any landing strips/airports, or under 700AGL if you are near certain larger airports. It is not legal to fly any manned aircraft in class g unless either transiting through to land/takeoff, or if you have clearance. However, it happens fairly often (just look at sightseeing helicopters as an example). A common problem with drone hobbyists is that they don't know anything about commercial airspace. Much of the concern has been about flying near airports where transiting low-altitude space is necessary. If drone operators had been assiduous in avoiding those areas (as RC aircraft operators have been) then this would be less of a concern. I agree though, that there is very little possibility of enforcing low altitude airspace rules, unless they force some kind of software/transponder system into use. even then, the home-built drones are just too easy to make to guarantee it.