About automatic planes -
I would not trust a fully automatic plane - someone could tamper with the computers and aircrafts are more mobile and harder to secure against unauthorised access than the nuclear plant from your example . Unfortunately there is little to do in this matter , maybe just a vote machine to the pax to open the door . Will not stop a determined individual to do something on approach / takeoff but it will prevent him crashing into a city or a nuclear plant for example .