I guess I don't feel that this will be the reason flying cars aren't adopted. In my mind, the barriers are almost entirely economics.
It's worth mentioning also that there seems to be a plan to have pilots for these programs in the near term. Take a look at Uber's Elevate concept video, there's a pilot on-board.
First, these cars would be easy targets for AA batteries. I would have to assume thst getting to close to a stadium full of people in one would lead to a shoot down, or remote shutdown.
Second, why bombs? What you can pack into a small aircraft is not the makings of a really impressive bomb, unless you have military grade high explosives. Now on the other hand, you could pack loads of nerve agents, chlorine, vessicants, or biological agents into one.
Third, you’d have to know enough about the hardware and software to modify it to fly empty, and violate restricted airspace. That might be a hell of a barrier to entry.
Fourth, these things could be heavily networked to function, so a rogue taxi could be taken over remotely, because it’s already remotely controlled.
Fifth, does the FBI care why you’re building a bomb or milling anthrax? Whatever your delivery system, they’re monitoring precursors and equipment you’d need. Air taxi, truck, drone, dudes with backpacks... the delivery system isn’t the chokepoint.
After all such cars will have to be self-flying. You're surely not suggesting the flying car using public would need to get a pilots license before flying in one ? That would already mean they're only a rich persons toy.
If the target is big enough (sports stadium for example) you.dont need to aim it. And as to why use a flying car instead of going there, I would have thought that was obvious. You can drop a car on people from a distance. Don't need to be there.