Maybe the problem is that commercial aircraft have pilots and manual controls that are always in threat of being taken over for sinister reasons. The technology exists to make future commercial A/C like drones that have pilots as a backup with control and pilot access being ultimately controlled from the ground. You cannot point an A/C at a building if you cannot take control even under the most violent conditions.
A less expensive and more practical solution would be to incorporate a 'safety-device' coupled with the EGPWS and the altimeter (like the EFA has) that takes over control from the pilot and corrects the A/C if it sees a conflict (advanced TCAS/EGPWS/AP type system) and therefore would prevent (via software) an A/C decending below a preset altitude in a software defined red area, (ie FL30 in NYC) such as urban cities if not on ILS LOC.
More of a problem on Boeing than Airbus but not impossible.
Only a thought!