Why not? What is the crucial difference, from the unauthorised intrusion POV? "This should not happen, therefore it cannot happen" is not an appropriate response here. http://www.infosecisland.com/blogview/16696-FACT-CHECK-SCADA...

(Note that I didn't mention anything about webservers, or Internet; are you sure the in-flight entertainment systems are separated from the control network by anything else than a firewall rule? See other embedded systems, and how secure they are. Start with...IDK, Toyota's gas pedal code, see how well such safety-critical code was written: https://users.ece.cmu.edu/~koopman/pubs/koopman14_toyota_ua_... )

Well, the problem with current state-of-the-art flight automation is that it can deal well with routine, repetitive tasks. What it fails at are corner cases (cf. US Airways Flight 1549), and self-diagnostics (sensor readings are inconsistent with current flight profile, e.g. Air France 447). In such cases, what you need is intelligence, not automatics.

This makes your argument another case of "let's assume we have strong AI; then pilotless aviation is easy-peasy." In other words, one of your unstated assumptions is still firmly in the realm of science fiction.