Three and a bit thousand posts on this thread have convinced me that:-
- Computers are better at accurate flying, humans are better at problem solving.
- Fully automated aircraft are not really viable/trustworthy yet, maybe never will be.
- Humans make mistakes sometimes, and just occasionally do some strange and tragic things, justified in only that one mind.
There is no way we can stop the occasional human error or the extremely rare murderous action. All of the solutions mentioned could be circumvented by a problem solving human. I think we just have to live with it as one of the very slight risks inherent in aviation, and virtually every other aspect of life. It is still safer than fully automated aircraft.