Your simple solution is not as clever as you think it is. The control software for quads knows where it is, where it can't go, and what happens to take it in any given direction. Even in fully automated mode the software I've used from 3 companies allows you to specify which direction a quad is facing and which direction it is flying at the same time. And on my own personal quad the geofence doesn't get easily defeated by flying backwards or flying sideways (my neighbour's 6 year old tried that, though not on purpose).
Also I didn't say anything about the ethics, just the technical details behind why it could work. I personally think the idea is wrong, very wrong.
Also while you're talking about complicated issues around airports, I believe the topic is the far more simple and more dubious case of "national security". There's not very many zones there and it could be defined using a single GPS point and a sphere model which is actually very little data.
The whole idea of blocking flights has another dubious issue. Just because you shouldn't fly in an area doesn't mean you can't ever fly in that area. I've flown within 200m of the airport at height. I would have been very pissed if some software locked me out, especially considering I had approval to do it from the airport operator to film a test of their new firefighting equipment.