A 'flying car' is heavy enough to do large amounts damage just by falling out of the sky. Doesn't have to have anyone riding in it to blow themselves up at the right time, a cell-phone triggered bomb will do just as well.
Molotov cocktail delivery vehicle? Why not? Requires a remote control lighter and remote release. How about dropping steel rebar? Needs tail fins for directional stability and some testing but that would be plenty troublesome. Drone mounted pistols are already here. (YouTube them.)
And yet the skies are considered safe enough today. I just think there are bigger concerns out there.
The only practical option is independent dual redundant power systems so that one failure can't take out more than half the propellers. Plus a rocket assisted ballistic recovery parachute to allow a (mostly) survivable crash landing in case of a catastrophic failure. Of course there will still be some rare failure modes where a parachute won't be sufficient.
3rd answer down :)
https://aviation.stackexchange.com/questions/37360/can-a-pas...
Rotor system inertia is incredibly important in autorotation, and this fact will pretty much make autorotation in quad+-rotor aircraft a no-go.
The only option here is a ballistic parachute / BRS, and personally that's not a system I'd stake my life on.
Loss of multiple rotors is perfectly manageable.
Add variable pitch blades and you get autorotation ability to handle total power loss.
Worrying about the threats posed is silly. A truck driven by a maniac still can do far more damage. No one is proposing a truck ban.